drm/nouveau/disp/gp102: fix cursor/overlay immediate channel indices

[ Upstream commit e50fcff1 ]

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>