drm/amd/powerplay: Remove unneeded variable 'result' in vega10_hwmgr.c

Fixes coccicheck warning:

drivers/gpu/drm/amd/powerplay/hwmgr/vega10_hwmgr.c:4363:5-11: Unneeded variable: "result". Return "0" on line 4370

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