mmc: dw_mmc-exynos: remove dw_mci_exynos_setup_clock

We combine what dw_mci_exynos_setup_clock does with init
hook to simplify the code

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>