[media] V4L: sh_mobile_csi2: fix unbalanced pm_runtime_put()

If the sh_mobile_csi2 driver didn't attach to a client, normally, because
the respective device connects to the SoC over the parallel CEU interface
and doesn't use the CSI-2 controller, it also shouldn't call
pm_runtime_put() on attempted disconnect.

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