[media] drivers/media/video/stk-webcam.c: webcam LED bug fix

The probem was on my DC-1125 webcam chip from Syntek. Whenever the webcam turns
on, the LED light on it is turn on also and never turns off again unless system
is shut downed or restarted.

This patch will fix this issue - the LED will be turned off whenever the device
is released.

Signed-off-by: Arvydas Sidorenko <asido4@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>