mmc: tmio: always start clock after frequency calculation

Starting the clock is always done after frequency change anyhow, so we can
do it directly after the clock calculation and remove the specific calls.
This is the first part of doing proper clock de-/activation at calculation
time.

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