Rename USB HOST pins (#1367)

Change “N” to “M” and add “HOST” in the USB pins. Only two pins are actually affected; diff appears large to maintain the pleasant aligned-columns format.

variants/adafruit_feather_usb_host/pins_arduino.h

@@ -14,8 +14,8 @@
 #define PIN_BUTTON      (7u)
 
 // USB host connector
-#define PIN_USB_DP     (16u)
-#define PIN_USB_DN     (17u)
+#define PIN_USB_HOST_DP (16u)
+#define PIN_USB_HOST_DM (17u)
 #define PIN_5V_EN       (18u)
 
 // Serial