powerpc/sbc8560: fix compile warning on CPM pin array

This is just a parallel of a5dc66e2
applied to the sbc8560 board.
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/platforms/85xx/sbc8560.c

@@ -156,7 +156,7 @@ static void __init init_ioports(void)
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(sbc8560_pins); i++) {
-		struct cpm_pin *pin = &sbc8560_pins[i];
+		const struct cpm_pin *pin = &sbc8560_pins[i];
 		cpm2_set_pin(pin->port, pin->pin, pin->flags);
 	}