[media] coda: Call v4l2_device_unregister() from a single location

Instead of calling v4l2_device_unregister() in multiple locations within the
error paths, let's call it from a single location to make the error handling
simpler.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>