[media] sh_mobile_csi2: fix module reloading

If the camera host driver (sh_mobile_ceu_camera.c) is unloaded and then
reloaded, probe will fail, because camera client .set_bus_param() and
.query_bus_param() methods have been set to NULL. Fix this by caching
the original pointers and restoring them on driver-unbind.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>