[media] media: mx2_camera: use managed functions to clean up code

Use managed functions to clean up the error handling code and function
mx2_camera_remove().  Along with the change, a few variables get removed
from struct mx2_camera_dev.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Tested-by: Javier Martin <javier.martin@vista-silicon.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>