mmc: tmio: use io* accessors consistently

Because we started using io*_rep accessors previously because they are
more widely defined across architectures, let's be consistent and use
this family for all accessor wrappers.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>