drm/amd/powerplay: Remove unneeded variable 'ret' in amdgpu_smu.c

Fixes coccicheck warning:

drivers/gpu/drm/amd/powerplay/amdgpu_smu.c:1192:5-8: Unneeded variable: "ret". Return "0" on line 1195
drivers/gpu/drm/amd/powerplay/amdgpu_smu.c:1945:5-8: Unneeded variable: "ret". Return "0" on line 1961

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>