sh_mobile_csi2: move it to the right place

	make[4]: *** No rule to make target `drivers/media/platform/sh_mobile_csi2.c',
	needed by `drivers/media/platform/sh_mobile_csi2.o'.  Stop.
Reported-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>