Fix sparse warnings. None are serious, but cutting down on these helps find
future serious sparse warnings/errors.

Redid the av7710.c patch based on a suggestion by Oliver Endriss.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>