ARM: dts: set display clock correctly for exynos4412-trats2

This patch sets display clock correctly. If Display clock isn't set
correctly then you would find below messages and Display controller
doesn't work correctly.

 exynos-drm: No connectors reported connected with modes
 [drm] Cannot find any crtc or sizes - going 1024x768

Fixes: abc0b144 ("drm: Perform basic sanity checks on probed modes")
Cc: <stable@vger.kernel.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Tested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>