ARM: ux500: Correct Snowball's external SD/MMC slot's bus width

Snowball's external SD/MMC slot is only capable of 4 bit data
transfer, not 8 bits as previously thought. This is a simple
fixup moving to the correct settings.
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

arch/arm/boot/dts/snowball.dts

@@ -123,7 +123,7 @@ ethernet@0 {
 		sdi0_per1@80126000 {
 			arm,primecell-periphid = <0x10480180>;
 			max-frequency = <50000000>;
-			bus-width = <8>;
+			bus-width = <4>;
 			mmc-cap-mmc-highspeed;
 			vmmc-supply = <&ab8500_ldo_aux3_reg>;