drm/amdgpu: Use unsigned ring indices in amdgpu_queue_mgr_map

commit fa7c7939 upstream.

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: effd924d ("drm/amdgpu: untie user ring ids from kernel ring ids v6")
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>