[media] coda/imx-vdoa: always wait for job completion

As long as only one CODA context is running we get alternating device_run()
and wait_for_completion() calls, but when more then one CODA context is
active, other VDOA slots can be inserted between those calls for one context.

Make sure to wait on job completion before running a different context and
before destroying the currently active context.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>