drm/qxl: release shadow on shutdown

drm/qxl: release shadow on shutdown

BugLink: https://bugs.launchpad.net/bugs/1928825
[ Upstream commit 4ca77c513537700d3fae69030879f781dde1904c ]

In case we have a shadow surface on shutdown release
it so it doesn't leak.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: http://patchwork.freedesktop.org/patch/msgid/20210204145712.1531203-6-kraxel@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>