[media] cx88: uninitialized variable

Fixes a gcc warning:

drivers/media/video/cx88/cx88-video.c:772:
	warning: ‘core’ may be used uninitialized in this function

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>