mmc: sh_mobile_sdhi: tidyup mmc_data->bus_shift for latest SoC

Latest SDHI on Renesas has expand register mapping.
update mmc_data->bus_shift for it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>