usbcas.h: don't use LED3; the Pro Micro board doesn't have it

The Leonardo board has 3 LEDs, but Pro Micro only has two

USBCAS/usbcas.h

@@ -52,13 +52,13 @@
 
 	/* Macros: */
 		/** LED mask for the library LED driver, to indicate that the USB interface is not ready. */
-		#define LEDMASK_USB_NOTREADY      LEDS_LED1
+		#define LEDMASK_USB_NOTREADY      (LEDS_LED1 | LEDS_LED2)
 
 		/** LED mask for the library LED driver, to indicate that the USB interface is enumerating. */
-		#define LEDMASK_USB_ENUMERATING  (LEDS_LED2 | LEDS_LED3)
+		#define LEDMASK_USB_ENUMERATING  (LEDS_LED1)
 
 		/** LED mask for the library LED driver, to indicate that the USB interface is ready. */
-		#define LEDMASK_USB_READY        (LEDS_LED2 | LEDS_LED4)
+		#define LEDMASK_USB_READY        (LEDS_LED2)
 
 		/** LED mask for the library LED driver, to indicate that an error has occurred in the USB interface. */
 		#define LEDMASK_USB_ERROR        (LEDS_LED1 | LEDS_LED3)