mmc: core: Add missing documetation for 'mmc' and 'ios'

mmc: core: Add missing documetation for 'mmc' and 'ios'

Remainder of the kerneldoc descriptions look present and correct.

Fixes the following W=1 kernel build warnings:

 drivers/mmc/core/regulator.c:178: warning: Function parameter or member 'mmc' not described in 'mmc_regulator_set_vqmmc'
 drivers/mmc/core/regulator.c:178: warning: Function parameter or member 'ios' not described in 'mmc_regulator_set_vqmmc'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200701124702.908713-4-lee.jones@linaro.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>