[media] MEDIA: ttusbir, fix double free

rc_unregister_device already calls rc_free_device to free the passed
device. But in one of ttusbir's probe fail paths, we call
rc_unregister_device _and_ rc_free_device. This is wrong and results
in a double free.
Instead, set rc to NULL resulting in rc_free_device being a noop.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>