ARM: dts: Fix gmac clock ids due to changes in Exynos5440

The Exynos5440 common clock driver has changed the clock ID's for
some of the clocks. Fix the gmac clock entries in Exynos5440 dtsi
file accordingly.

Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>