ARM: dts: uniphier: fix pin groups of eMMC pin-mux node

The eMMC devices on UniPhier boards are generally used in the 8-bit
mode.  So, DAT4-7 pins should be controlled.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

arch/arm/boot/dts/uniphier-pinctrl.dtsi

@@ -45,7 +45,7 @@
 
 &pinctrl {
 	pinctrl_emmc: emmc_grp {
-		groups = "emmc";
+		groups = "emmc", "emmc_dat8";
 		function = "emmc";
 	};