Initialize local variable with smth meaningful

I prefer explicit INVALID rather than possible compiler warning about uninitialized var sometimes later

Author: iakov

mac/hid.c

@@ -694,7 +694,7 @@ hid_device * HID_API_EXPORT hid_open_path(const char *path)
 {
 	hid_device *dev = NULL;
 	io_registry_entry_t entry = MACH_PORT_NULL;
-	IOReturn ret;
+	IOReturn ret = kIOReturnInvalid;
 
 	dev = new_hid_device();