ARM: dts: fix incorrect ak8975 compatible for exynos4412-trats2 board

This patch fixed incorrect compatible for ak8975 magnetic sensor.
ak8975 magnetic sensor use compatible "ak8975" or "asahi-kasei,ak8975"
In this patch, use "asahi-kasei,ak8975" according to dt bindings document.

Signed-off-by: Beomho Seo <beomho.seo@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>