media: venus: match instance creation and destruction order

Match order of instances' initialization in venc_open()/vdec_close()
and order of destruction in venus_common_close().

Suggested-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Stanimir Varbanov <stanimir.k.varbanov@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>