Exynos5: Fix exynos5_get_periph_rate calculations

exynos5_get_periph_rate function reads incorrect div for
SDMMC2 & 3. It also reads prediv and does division only for
SDMMC0 & 2 when actually various other peripherals need that.
Adding changes to fix these mistakes in periph rate calculation.

Signed-off-by: Akshay Saraswat <akshay.s@samsung.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>