mfd: mmc: rtsx: Change default tx phase

The default phase can meet most cards' requirement, but it is not the
optimal one. In some extreme situation, the rx phase point produced by
the following tuning process will drift quite a distance.
Before tuning UHS card, this patch will set a more proper initial tx
phase point, which is calculated from statistic data, and can achieve
a much better tx signal quality.

Signed-off-by: Wei WANG <wei_wang@realsil.com.cn>
Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Chris Ball <cjb@laptop.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>