CHROMIUM: virtio: video: Cancel worker on release

Prior this patch, if a v4l2_m2m_ctx_release was called between queueing
worker and it's execution, the worker would try to lock on an NULL
mutex, causing kernel crash.

This patch cancels a rending worker, before releasing an
v4l2_m2m_ctx.

Signed-off-by: Bartłomiej Grzesik <bag@semihalf.com>

BUG=b:245795223
TEST=None

Change-Id: I23f82d9409ca2c7d528df16f999c7ec32f75e91a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/4106180


Tested-by: Bartłomiej Grzesik <bag@semihalf.com>
Reviewed-by: Marcin Wojtas <mwojtas@google.com>
Auto-Submit: Bartłomiej Grzesik <bag@semihalf.com>
Commit-Queue: Marcin Wojtas <mwojtas@google.com>
Signed-off-by: Slawomir Rosek <srosek@google.com>