mmc: mediatek: Drop pointer to mmc_host from msdc_host

mmc: mediatek: Drop pointer to mmc_host from msdc_host

The MediaTek MMC driver uses  pointer to get from private
msdc_host structure to the generic mmc_host structure.
However mmc_host always precedes msdc_host in memory so compute
its address with a subtraction (which is cheaper than a dereference)
using mmc_from_priv() and drop the extra pointer.

Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com>
Link: https://lore.kernel.org/r/20200917192624.548720-1-ameynarkhede03@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>