Hid: wacom: Fix kernel test robot warning

Kernel test robot throws the following warning -
>> drivers/hid/wacom_wac.c:2411:42: warning: format specifies type 'unsigned short' but the argument has type 'int' [-Wformat]
                           hid_warn(hdev, "Dropped %hu packets", value - wacom_wac->hid_data.sequence_number);
                                                   ~~~           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                                   %d

Explicitly casting the argument to unsigned short to silence the warning and retain the intended behavior.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Joshua Dickens <joshua.dickens@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/wacom_wac.c

@@ -2408,7 +2408,7 @@ static void wacom_wac_pen_event(struct hid_device *hdev, struct hid_field *field
 		return;
 	case WACOM_HID_WD_SEQUENCENUMBER:
 		if (wacom_wac->hid_data.sequence_number != value)
-			hid_warn(hdev, "Dropped %hu packets", value - wacom_wac->hid_data.sequence_number);
+			hid_warn(hdev, "Dropped %hu packets", (unsigned short)(value - wacom_wac->hid_data.sequence_number));
 		wacom_wac->hid_data.sequence_number = value + 1;
 		return;
 	}