mmc: dw_mmc: move the platform specific init call

Current platform specific private data initialization call
dw_mci_exynos_priv_init() can be used to do platform specific
initialization of SMU and others in future. So the drv_data->init
call has moved to dw_mci_probe().

Signed-off-by: Yuvaraj Kumar C D <yuvaraj.cd@samsung.com>
Tested-by: Alim Akhtar <alim.akhtar@samsung.com>
Tested-by: Jaehoon Chung <jh80.chung@samsung.com>
Acked-by: Seungwon Jeon <tgih.jun@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>