V4L/DVB (8561): make ivtv_claim_stream() static

ivtv_claim_stream() can now become static.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>