mmc: tmio: use ioread* for repeated access to a register

Not all archs define reads* and writes*. Switch to ioread*_rep and
friends which is defined everywhere, so we can enable COMPILE_TEST after
that.

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