HID: wacom: leds: Don't try to control the EKR's read-only LEDs

Commit a50aac7 introduces 'led.groups' and adds EKR support
for these groups. However, unlike the other devices with LEDs,
the EKR's LEDs are read-only and we shouldn't attempt to control
them in wacom_led_control().

See bug: https://sourceforge.net/p/linuxwacom/bugs/342/

Fixes: a50aac7 ("HID: wacom: leds: dynamically allocate LED groups")
Cc: stable <stable@vger.kernel.org>     # 4.9
Signed-off-by: Aaron Armstrong Skomra <aaron.skomra@wacom.com>
Reviewed-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/wacom_sys.c

@@ -766,6 +766,9 @@ static int wacom_led_control(struct wacom *wacom)
 	if (!wacom->led.groups)
 		return -ENOTSUPP;
 
+	if (wacom->wacom_wac.features.type == REMOTE)
+		return -ENOTSUPP;
+
 	if (wacom->wacom_wac.pid) { /* wireless connected */
 		report_id = WAC_CMD_WL_LED_CONTROL;
 		buf_size = 13;