drm/nouveau/pm: allow zeroed signals to enable sources
drm/nouveau/pm: allow zeroed signals to enable sources

Hardware signals index 0x00 are defined for some domains and they have
to be allowed to enable sources like the others.

Signed-off-by: Samuel Pitoiset <506e97eed81d9e59d22f4c73fb51123bb62b4a30@gmail.com>
Signed-off-by: Ben Skeggs <d9f27fb07c1e9f131223ad827fa5179f3846c30b@redhat.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs