drm/amdgpu: Fix code style issue

drm/amdgpu: Fix code style issue

cocci warnings: (new ones prefixed by >>)
>> drivers/gpu/drm/amd/amdgpu/amdgpu_device.c:6088:8-9:
Unneeded variable: "r". Return "0" on line 6141

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202506281925.HHIpXiO7-lkp@intel.com/
Signed-off-by: Ce Sun <cesun102@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>