[media] coda: fix error path in case of missing pdata on non-DT platform

If we bail out this early, v4l2_device_register() has not been called
yet, so no need to call v4l2_device_unregister().

Fixes: b7bd660a ("[media] coda: Call v4l2_device_unregister() from a single location")

Reported-by: Michael Olbrich <m.olbrich@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>