ARM: dts: fix clock-frequency of display timing0 for exynos3250-rinato

After the commit abc0b144 ("drm: Perform basic sanity checks on
probed modes"), proper clock-frequency becomes mandatory for
validating the mode of panel.  The display does not work if there is
no mode validated. Also, this clock-frequency must be set
appropriately for getting required frame rate.

Fixes: abc0b144 ("drm: Perform basic sanity checks on probed modes")
Cc: <stable@vger.kernel.org>
Signed-off-by: Hyungwon Hwang <human.hwang@samsung.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Sigend-off-by: Kukjin Kim <kgene@kernel.org>