drm/qxl: properly handle device init failures

Specifically do not try release resources which where
not allocated in the first place.

Cc: Tong Zhang <ztong0001@gmail.com>
Tested-by: Tong Zhang <ztong0001@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: http://patchwork.freedesktop.org/patch/msgid/20210217123213.2199186-2-kraxel@redhat.com