drm/nouveau: rename nouveau_drm.h to nouveau_drv.h

Fixes out-of-tree build issue where uapi/drm/nouveau_drm.h gets picked
up instead.

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

drivers/gpu/drm/nouveau/nouveau_sgdma.c

@@ -1,7 +1,7 @@
 #include <linux/pagemap.h>
 #include <linux/slab.h>
 
-#include "nouveau_drm.h"
+#include "nouveau_drv.h"
 #include "nouveau_ttm.h"
 
 struct nouveau_sgdma_be {