[media] pwc: Remove unneeded struct vb2_queue clearing

struct vb2_queue is allocated through kzalloc as part of a larger struct,
there's no need to clear it.

Cc: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Ezequiel Garcia <elezegarcia@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>