mmc: sdhci: Add out_unlock to sdhci_execute_tuning

A 'goto' can be used to save duplicating unlocking
and returning.

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