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

This is an improved version of the patch I sent a little ago.

The problem was:
	On my DC-1125 webcam chip from Syntek, whenever the webcam turns
	on, the LED light on it is turned on also and never turns off again unless
	system is shut downed or restarted.

The previous version seemed to break some other laptop webcam work. Thanks
to Andrea Anacleto for the bug report and solution.

Signed-off-by: Andrea Anacleto <andreaanacleto@libero.it>
Signed-off-by: Arvydas Sidorenko <asido4@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>