drm/amd/powerplay: suppress the kernel test robot warning

Suppress the warning below:
   In file included from drivers/gpu/drm/amd/amdgpu/../powerplay/smu_cmn.c:
>> drivers/gpu/drm/amd/powerplay/smu_cmn.c:485:9: warning: Identical condition 'ret', second condition is always false [identicalConditionAfterEarlyExit]
    return ret;
           ^
   drivers/gpu/drm/amd/powerplay/smu_cmn.c:477:6: note: first condition
    if (ret)
        ^
   drivers/gpu/drm/amd/powerplay/smu_cmn.c:485:9: note: second condition
    return ret;
           ^

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>