drm/amd/amdgpu: Fix return values in SI DPM code

Fix a couple of spots where errors were not returned as
well as add some error messages to
si_patch_dependency_based_on_leakage() which were not being
read.

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>