[media] v4l: omap3isp: Don't check for missing get_fmt op on remote subdev

The remote subdev of any video node in the OMAP3 ISP is an internal
subdev that is guaranteed to implement get_fmt. Don't check the return
value for -ENOIOCTLCMD, as this can't happen.
While at it, move non-critical code out of the mutex-protected section.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>