drm/amdgpu: refine code for code style.

White space fix.
Signed-off-by: NRex Zhu <Rex.Zhu@amd.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>