renderonly: drop resources on destroy

renderonly: drop resources on destroy

The renderonly_scanout holds a reference on its prime pipe resource,
which should be released when it is destroyed. If it was created by
renderonly_create_kms_dumb_buffer_for_resource, the dumb BO also has
to be destroyed.

Fixes: 848b49b288f ("gallium: add renderonly library")
CC: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>