drm/amdgpu: Use unsigned ring indices in amdgpu_queue_mgr_map

drm/amdgpu: Use unsigned ring indices in amdgpu_queue_mgr_map

This matches the corresponding UAPI fields. Treating the ring index as
signed could result in accessing random unrelated memory if the MSB was
set.

Fixes: 788903a9d9b2 ("drm/amdgpu: untie user ring ids from kernel ring
                      ids v6")
Cc: stable@vger.kernel.org
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>