drm/amdgpu: fix vcn doorbell range setting

Should use vcn_ring0_1 instead of doorbell index to
set nbio doorbell range.

Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: Sonny Jiang <sonny.jiang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>