drm/amdgpu: fix error return code in mes_v12_1_map_test_bo

drm/amdgpu: fix error return code in mes_v12_1_map_test_bo

The function mes_v12_1_map_test_bo incorrectly returned 0 unconditionallyon error path,
which would hide the real error code and mislead upperlayers about the failure status.
Fix it by returning the correct error code 'r' instead of 0.

Fixes: 44e5195fa3d4 ("drm/amdgpu/mes_v12_1: add mes self test");
Signed-off-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Asad Kamal <asad.kamal@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>