drm/amd/display: Correctly cancel future watchdog and callback events

[Why]
-We need to cancel future callbacks/watchdogs events when a callback/watchdog event happens

[How]
-fix typo in event_callback()
	-cancel callback, not watchdog
-cancel watchdog events in event_watchdog_timer().

Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>