v4l2videodec: Add lock for queue and stream off

Add lock for queue and stream off, or v4l2 core will complain it.
Remove sink event task stop as flush() will do the same.

https://bugzilla.gnome.org/show_bug.cgi?id=752962

UpStream Status: Pending

Signed-off-by: Song Bing<bing.song@nxp.com>
2 files changed