[media] V4L2: mx3_camera: convert to managed resource allocation

Use devm_* resource allocators to simplify the driver's probe and clean up
paths.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>