drm/amd/pm: fix the return value of pm message

0 should be right driver return value, 0x1 is the right firmware
return value. So switch to 0 at last.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Xiaojian Du <xiaojian.du@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>