queue_init() is always called by v4l2_m2m_ctx_init(), which allocates
a context struct v4l2_m2m_ctx with kzalloc.
Therefore, there is no need to clear vb2_queue src/dst structs.

Cc: Javier Martin <javier.martin@vista-silicon.com>
Signed-off-by: Ezequiel Garcia <elezegarcia@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>