ARM: dts: exynos5250: Fix MDMA0 clock number

Due to incorrect clock specified in MDMA0 node, using MDMA0 controller
could cause system failures, due to wrong clock being controlled. This
patch fixes this by specifying correct clock.

Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
[t.figa: Corrected commit message and description.]
Signed-off-by: Tomasz Figa <t.figa@samsung.com>