drm/amdgpu: update uvd_v6_0_ring_vm_funcs to use new nop packet

Was missed when updating the uvd 6 module.

Fixes: 1aac3c91 (drm/amdgpu: fix insert nop for UVD6 ring)
Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org