Change USB NULL errors to short strings

shared-module/usb/core/Device.c had several spots where it would
raise a MicroPython exception with a NULL argument. That made it
very difficult for CircuitPython code to attempt to recover from
fault conditions caused by quirky USB device behavior. This adds
short error strings to distinguish the different types of faults.

Author: samblenny

shared-module/usb/core/Device.c

@@ -159,7 +159,7 @@ static size_t _xfer(tuh_xfer_t *xfer, mp_int_t timeout) {
     _xfer_result = 0xff;
     xfer->complete_cb = _transfer_done_cb;
     if (!tuh_edpt_xfer(xfer)) {
-        mp_raise_usb_core_USBError(NULL);
+        mp_raise_usb_core_USBError(MP_ERROR_TEXT("Xfer"));
     }
     uint32_t start_time = supervisor_ticks_ms32();
     while ((timeout == 0 || supervisor_ticks_ms32() - start_time < (uint32_t)timeout) &&
@@ -176,7 +176,7 @@ static size_t _xfer(tuh_xfer_t *xfer, mp_int_t timeout) {
     xfer_result_t result = _xfer_result;
     _xfer_result = 0xff;
     if (result == XFER_RESULT_STALLED) {
-        mp_raise_usb_core_USBError(MP_ERROR_TEXT("Pipe error"));
+        mp_raise_usb_core_USBError(MP_ERROR_TEXT("Stall"));
     }
     if (result == 0xff) {
         tuh_edpt_abort_xfer(xfer->daddr, xfer->ep_addr);
@@ -205,7 +205,7 @@ static bool _open_endpoint(usb_core_device_obj_t *self, mp_int_t endpoint) {
     }
 
     if (self->configuration_descriptor == NULL) {
-        mp_raise_usb_core_USBError(MP_ERROR_TEXT("No configuration set"));
+        mp_raise_usb_core_USBError(MP_ERROR_TEXT("NoCfg"));
     }
 
     tusb_desc_configuration_t *desc_cfg = (tusb_desc_configuration_t *)self->configuration_descriptor;
@@ -239,7 +239,8 @@ static bool _open_endpoint(usb_core_device_obj_t *self, mp_int_t endpoint) {
 
 mp_int_t common_hal_usb_core_device_write(usb_core_device_obj_t *self, mp_int_t endpoint, const uint8_t *buffer, mp_int_t len, mp_int_t timeout) {
     if (!_open_endpoint(self, endpoint)) {
-        mp_raise_usb_core_USBError(NULL);
+        mp_raise_usb_core_USBError(MP_ERROR_TEXT("Endpt"));
+        return 0;
     }
     tuh_xfer_t xfer;
     xfer.daddr = self->device_number;
@@ -251,7 +252,8 @@ mp_int_t common_hal_usb_core_device_write(usb_core_device_obj_t *self, mp_int_t
 
 mp_int_t common_hal_usb_core_device_read(usb_core_device_obj_t *self, mp_int_t endpoint, uint8_t *buffer, mp_int_t len, mp_int_t timeout) {
     if (!_open_endpoint(self, endpoint)) {
-        mp_raise_usb_core_USBError(NULL);
+        mp_raise_usb_core_USBError(MP_ERROR_TEXT("Endpt"));
+        return 0;
     }
     tuh_xfer_t xfer;
     xfer.daddr = self->device_number;
@@ -285,7 +287,7 @@ mp_int_t common_hal_usb_core_device_ctrl_transfer(usb_core_device_obj_t *self,
     _xfer_result = 0xff;
 
     if (!tuh_control_xfer(&xfer)) {
-        mp_raise_usb_core_USBError(NULL);
+        mp_raise_usb_core_USBError(MP_ERROR_TEXT("Xfer"));
     }
     uint32_t start_time = supervisor_ticks_ms32();
     while ((timeout == 0 || supervisor_ticks_ms32() - start_time < (uint32_t)timeout) &&
@@ -302,7 +304,7 @@ mp_int_t common_hal_usb_core_device_ctrl_transfer(usb_core_device_obj_t *self,
     xfer_result_t result = _xfer_result;
     _xfer_result = 0xff;
     if (result == XFER_RESULT_STALLED) {
-        mp_raise_usb_core_USBError(MP_ERROR_TEXT("Pipe error"));
+        mp_raise_usb_core_USBError(MP_ERROR_TEXT("Stall"));
     }
     if (result == 0xff) {
         tuh_edpt_abort_xfer(xfer.daddr, xfer.ep_addr);