drm/nouveau/svm: fix migrate page regression

The patch to add zero page migration to GPU memory inadvertently included
part of a future change which broke normal page migration to GPU memory
by copying too much data and corrupting GPU memory.
Fix this by only copying one page instead of a byte count.

Fixes: 9d4296a7 ("drm/nouveau/nouveau/hmm: fix migrate zero page to GPU")
Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_dmem.c

@@ -550,7 +550,7 @@ static unsigned long nouveau_dmem_migrate_copy_one(struct nouveau_drm *drm,
 					 DMA_BIDIRECTIONAL);
 		if (dma_mapping_error(dev, *dma_addr))
 			goto out_free_page;
-		if (drm->dmem->migrate.copy_func(drm, page_size(spage),
+		if (drm->dmem->migrate.copy_func(drm, 1,
 			NOUVEAU_APER_VRAM, paddr, NOUVEAU_APER_HOST, *dma_addr))
 			goto out_dma_unmap;
 	} else {