drm/amd/pm: fix return value in aldebaran_set_mp1_state()

For default cases,we should return 0. Otherwise resume will
abort because of the wrong return value.

Signed-off-by: Feifei Xu <Feifei.Xu@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>