clk: exynos5250: Fix divider values for sclk_mmc{0,1,2,3}

In legacy setup, sclk_mmc{0,1,2,3} used PRE_RATIO bit-field (8-bit wide)
instead of RATIO bit-field (4-bit wide) for dividing clock rate.

With current common clock setup, we are using RATIO bit-field which
is creating FIFO read errors while accessing eMMC. Changing over to
use PRE_RATIO bit-field fixes this issue.

dwmmc_exynos 12200000.dwmmc0: data FIFO error (status=00008020)
mmcblk0: error -5 transferring data, sector 1, nr 7, cmd response 0x900, card status 0x0
end_request: I/O error, dev mmcblk0, sector 1

Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
CC: Thomas Abraham <thomas.abraham@linaro.org>
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>