drm/amdgpu: free the metadata buffer for sg type BOs as well

Since both sg and device type BOs have metadata buffer, free
the buffer in both cases when to destroy BOs

Signed-off-by: Shiwu Zhang <shiwu.zhang@amd.com>
Acked-by: Nirmoy Das <Nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>