USBHost: Silence unused variable warnings.

I removed the initialization of some variables which were never used to
silence GCC warnings.

One of them had me removing the following line from
USBHostMouse::rxHandler():
    int len = int_in->getLengthTransferred();
The variable len is never used again in this method and it doesn't
appear that the int_in->getLengthTransferred() call has any side
effects which would require this extraneous call to remain in the code.

Author: adamgreen

libraries/USBHost/USBHostHID/USBHostMouse.cpp

@@ -82,7 +82,6 @@ bool USBHostMouse::connect() {
 
 void USBHostMouse::rxHandler() {
     int len_listen = int_in->getSize();
-    int len = int_in->getLengthTransferred();
 
     if (onUpdate) {
         (*onUpdate)(report[0] & 0x07, report[1], report[2], report[3]);

libraries/USBHost/USBHostSerial/USBHostSerial.cpp

@@ -131,10 +131,10 @@ void USBHostSerial::format(int bits, Parity parity, int stop_bits) {
     line_coding.stop_bits = (stop_bits == 1) ? 0 : 2;
 
     // set line coding
-    int res = host->controlWrite(   dev,
-                                    USB_RECIPIENT_INTERFACE | USB_HOST_TO_DEVICE | USB_REQUEST_TYPE_CLASS,
-                                    SET_LINE_CODING,
-                                    0, serial_intf, (uint8_t *)&line_coding, 7);
+    host->controlWrite( dev,
+                        USB_RECIPIENT_INTERFACE | USB_HOST_TO_DEVICE | USB_REQUEST_TYPE_CLASS,
+                        SET_LINE_CODING,
+                        0, serial_intf, (uint8_t *)&line_coding, 7);
 }
 
 int USBHostSerial::_getc() {