[media] v4l: omap4iss: Move common code out of switch...case

Code common to all cases can be moved out of the switch...case
statement.

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>