[media] v4l: omap4iss: Simplify error paths

Get rid of a goto statement for a simple error path that can be inlined,
and split spaghetti error code to a separate section.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>