drm/nouveau: workaround semaphore hw bug causing unnecessary interrupts

The HW will only accept the DMA_FROM_MEMORY class for DMA_SEMAPHORE without
asking the driver to intervene.

It appears that semaphores will work correctly even without DMA_IN_MEMORY,
so lets avoid the large amount of interrupts generated by x-chan sync.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_fence.c

@@ -519,7 +519,7 @@ nouveau_fence_channel_init(struct nouveau_channel *chan)
 	if (USE_SEMA(dev) && dev_priv->chipset < 0x84) {
 		struct ttm_mem_reg *mem = &dev_priv->fence.bo->bo.mem;
 
-		ret = nouveau_gpuobj_dma_new(chan, NV_CLASS_DMA_IN_MEMORY,
+		ret = nouveau_gpuobj_dma_new(chan, NV_CLASS_DMA_FROM_MEMORY,
 					     mem->start << PAGE_SHIFT,
 					     mem->size, NV_MEM_ACCESS_RW,
 					     NV_MEM_TARGET_VRAM, &obj);