HID: wacom: generic: sync pad events only for actual packets

Commits d793ff8 and 4082da8 introduced two pad usages which do not
actually send pad input events. To make sure we do not post empty
pad packets, pad_input_event_flag is introduced. Turn on the flag
for real pad input events so we can synchronize them properly.

Signed-off-by: Ping Cheng <ping.cheng@wacom.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/hid/wacom_wac.h b/drivers/hid/wacom_wac.h
index 839bd4b..570d295 100644
--- a/drivers/hid/wacom_wac.h
+++ b/drivers/hid/wacom_wac.h
@@ -301,6 +301,7 @@
 	int bat_charging;
 	int bat_connected;
 	int ps_connected;
+	bool pad_input_event_flag;
 };
 
 struct wacom_remote_data {