mmc: meson-gx: fix rx phase reset

Resetting the phase when POWER_ON is set the set_ios() call means that the
phase is reset almost every time the set_ios() is called, while the
expected behavior was to reset the phase on a power cycle.

This had gone unnoticed until now because in all mode (except hs400) the
tuning is done after the last to set_ios(). In such case, the tuning
result is used anyway.  In HS400, there are a few calls to set_ios() after
the tuning is done, overwriting the tuning result.

Resetting the phase on POWER_UP instead of POWER_ON solve the problem.

Fixes: d341ca88

 ("mmc: meson-gx: rework tuning function")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>