mmc: sdhci: Always init buf_ready_int

There is no point making the initialization
of buf_ready_int conditional on host version.
Simplify by just doing it always. Note that
the other conditional initializations will be
removed when the new way of doing re-tuning
is taken into use.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>