mmc: exynos_dw_mmc: add the error control for checking index

mmc: exynos_dw_mmc: add the error control for checking index

PERIPH_ID_SDMMC4(131) is not continous value with PERIPH_ID_SDMMC0(75).
If there is no 'index' property in fdt, then dev_index should be
assigned to dev_id(Peripheral ID).
At this time, dev_index should be "56". It means Exynos SoC has "56"
numbers of DWMMC IP. To prevent this behavior, it needs to check the
maximum device index.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>