[media] soc_camera: Use module_platform_driver macro

module_platform_driver simplifies the code by eliminating
module_init and module_exit calls.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>