HID: fix pad button definition in hid-wacom

This fix is required for xorg driver to recognise 2 pad buttons

Signed-off-by: Przemo Firszt <przemo@firszt.eu>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/hid/hid-wacom.c b/drivers/hid/hid-wacom.c
index 7475421..75ea66a 100644
--- a/drivers/hid/hid-wacom.c
+++ b/drivers/hid/hid-wacom.c
@@ -196,6 +196,9 @@
 	/* Pad */
 	input->evbit[0] |= BIT(EV_MSC);
 	input->mscbit[0] |= BIT(MSC_SERIAL);
+	set_bit(BTN_0, input->keybit);
+	set_bit(BTN_1, input->keybit);
+	set_bit(BTN_TOOL_FINGER, input->keybit);
 
 	/* Distance, rubber and mouse */
 	input->absbit[0] |= BIT(ABS_DISTANCE);