ARM: dts: fix compatible value for exynos pinctrl

Fix the incorrect compatible property value of pinctrl for EXYNOS4 SoCs.

Cc: Thomas Abraham <thomas.ab@samsung.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>