drm/amd/powerplay: minor fixes around SW SMU power and fan setting

Add checking for possible invalid input and null pointer. And
drop redundant code.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
2 files changed