mmc: sh_mmcif: separate sh_mmcif_clk_update() into setup and prepare

Current sh_mmcif_clk_update() is called from probe() and set_ios(),
but, the purpose of later one is just clk_prepare_enable().
No need to setup mmc->f_max/f_min in many times.
This patch separe sh_mmcif_clk_update() into clk_prepare_enable()
and mmc->f_max/f_min setup.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Keita Kobayashi <keita.kobayashi.ym@renesas.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>