drm/nouveau/mpeg: mthd returns true on success now

commit 83bce9c2 upstream.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Fixes: 590801c1 ("drm/nouveau/mpeg: remove dependence on namedb/engctx lookup")
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>