clk: samsung: exynos4: Correct SRC_MFC register

The SRC_MFC register offset was incorrect, which could cause have caused
wrong calculation of rate of sclk_mfc clock, that could in turn lead to
incorrect operation of MFC. This patch corrects it.

Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
[t.figa: Updated patch description]
Signed-off-by: Tomasz Figa <t.figa@samsung.com>