According to the App note[1] detailing the tuning algorithm, for
temperatures < -20C, the initial tuning value should be min(largest value
in LPW - 24, ceil(13/16 ratio of LPW)). The largest value in LPW is
(max_window + 4 * (max_len - 1)) and not (max_window + 4 * max_len) itself.
Fix this implementation.

[1] http://www.ti.com/lit/an/spraca9b/spraca9b.pdf

Fixes: 961de0a8 ("mmc: sdhci-omap: Workaround errata regarding SDR104/HS200 tuning failures (i929)")
Cc: stable@vger.kernel.org
Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>