drm/nouveau/pm: fix compilation failure when CONFIG_POWER_SUPPLY is not set

Signed-off-by: Martin Peres <martin.peres@ensi-bourges.fr>
Reported-by: Stratos Psomadakis <psomas@ece.ntua.gr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
1 file changed