powerpc/85xx/mpc85xx_ds: Don't use the flat device-tree after boot

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/85xx/mpc85xx_ds.c

@@ -66,9 +66,7 @@ void __init mpc85xx_ds_pic_init(void)
 	struct device_node *cascade_node = NULL;
 	int cascade_irq;
 #endif
-	unsigned long root = of_get_flat_dt_root();
-
-	if (of_flat_dt_is_compatible(root, "fsl,MPC8572DS-CAMP")) {
+	if (of_machine_is_compatible("fsl,MPC8572DS-CAMP")) {
 		mpic = mpic_alloc(NULL, 0,
 			MPIC_NO_RESET |
 			MPIC_BIG_ENDIAN |