[media] V4L2: platform: rcar_jpu: switch off clock on release later

Give JPU peripheral chance to finish current job.
Don't switch off clock until context release.

Signed-off-by: Mikhail Ulyanov <mikhail.ulyanov@cogentembedded.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>