drm/nouveau/mc: fix race condition between constructor and request_irq()

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

diff --cc drivers/gpu/drm/nouveau/core/include/subdev/mc.h
Simple merge

diff --cc drivers/gpu/drm/nouveau/core/subdev/mc/base.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/core/subdev/mc/nv04.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/core/subdev/mc/nv44.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/core/subdev/mc/nv50.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/core/subdev/mc/nv98.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/core/subdev/mc/nvc0.c
Simple merge