mmc: sh_mmcif: add sh_mmcif_host_to_dev() macro and use it.

Current sh_mmcif driver is directly using &host->pd->dev in all place.
It is not big problem, but it is unreadable, and it can be cause of
future bug. This patch adds new sh_mmcif_host_to_dev() and use it.
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Keita Kobayashi <keita.kobayashi.ym@renesas.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>