V4L/DVB (8748): V4L: fix return value of meye probe callback

The return vaule of the probe function should return -ENOMEM instead
of -EBUSY if video_device_alloc() fails.

Signed-off-by: Henrik Kretzschmar <henne@nachtwindheim.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>