drm/nv50: fix two potential suspend/resume oopses

This avoids touching the dummy channel 0/127 we have on nv50.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

diff --cc drivers/gpu/drm/nouveau/nouveau_drv.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/nv50_fifo.c
Simple merge