[media] V4L: mx1-camera: fix uninitialized variable

mx1_camera_add_device() can return an uninitialized value of ret.

Signed-off-by: Andre Bartke <andre.bartke@gmail.com>
[g.liakhovetski@gmx.de: modified the fix to remove "ret" completely]
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>