V4L/DVB: ov511: cleanup: remove unneeded null check

We dereference "ov" unconditionally throughout the function so there is
no way it can be NULL here.  This code has been around for ages so if
it were possible for "ov" to be NULL someone would have complained.

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