mmc: sdricoh_cs: Move MMC_APP_CMD handling to sdricoh_mmc_cmd()

Move MMC_APP_CMD specific handling to be managed by sdricoh_mmc_cmd(), as
this makes the code a bit cleaner.

Cc: Sascha Sommer <saschasommer@freenet.de>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20200414161413.3036-11-ulf.hansson@linaro.org