drm/nouveau/fifo/nvc0: bash some magic reg to make uevent interrupt work

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

drivers/gpu/drm/nouveau/core/engine/fifo/nvc0.c

@@ -706,6 +706,7 @@ nvc0_fifo_init(struct nouveau_object *object)
 	nv_wr32(priv, 0x002a00, 0xffffffff); /* clears PFIFO.INTR bit 30 */
 	nv_wr32(priv, 0x002100, 0xffffffff);
 	nv_wr32(priv, 0x002140, 0x3fffffff);
+	nv_wr32(priv, 0x002628, 0x00000001); /* makes mthd 0x20 work */
 	return 0;
 }