HID: wacom: leds: make sure Cintiq 21UX2 and 24HD control the right LEDs

The code for 21UX2 and 24HD makes the LED group 1 on the left, and
the group 0 on the right. The buttons are ordered in the other way,
but libwacom already exports those that way. So we simply can't reassign
LED group 0 to the left buttons, and have to quirk the incoming data...
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/wacom_wac.c

@@ -2768,6 +2768,15 @@ static bool wacom_is_led_toggled(struct wacom *wacom, int button_count,
 {
 	int button_per_group;
 
+	/*
+	 * 24HD and 21UX2 have LED group 1 to the left and LED group 0
+	 * to the right. We need to reverse the group to match this
+	 * historical behavior.
+	 */
+	if (wacom->wacom_wac.features.type == WACOM_24HD ||
+	    wacom->wacom_wac.features.type == WACOM_21UX2)
+		group = 1 - group;
+
 	button_per_group = button_count/wacom->led.count;
 
 	return mask & (1 << (group * button_per_group));