[POWERPC] 85xx: Fix compile warning

arch/powerpc/platforms/85xx/mpc85xx_ads.c: In function ‘init_ioports’:
arch/powerpc/platforms/85xx/mpc85xx_ads.c:168: warning: initialization discards qualifiers from pointer target type
Signed-off-by: NKumar Gala <galak@kernel.crashing.org>

arch/powerpc/platforms/85xx/mpc85xx_ads.c

@@ -165,7 +165,7 @@ static void __init init_ioports(void)
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(mpc8560_ads_pins); i++) {
-		struct cpm_pin *pin = &mpc8560_ads_pins[i];
+		const struct cpm_pin *pin = &mpc8560_ads_pins[i];
 		cpm2_set_pin(pin->port, pin->pin, pin->flags);
 	}