[media] mem2mem: make queue lock in v4l2_m2m_poll interruptible

This patch makes the queue lock taken in v4l2_m2m_poll interruptible.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>