drm/nouveau: Fix runtime PM leak in drm_open()

drm/nouveau: Fix runtime PM leak in drm_open()

Noticed this as I was skimming through, if we fail to allocate memory
for cli we'll end up returning without dropping the runtime PM ref we
got. Additionally, we'll even return the wrong return code! (ret most
likely will == 0 here, we want -ENOMEM).

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>