drm/amdgpu: fix memory leak in mes self test

The fences associated with mes queue have to be freed
up during amdgpu_ring_fini.

Signed-off-by: Jack Xiao <Jack.Xiao@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>