mmc: sdhci-omap: Remove redundant structure assignments

The sdhci_execute_tuning() function has assignment of
private pointers multiple times. Remove the redundant assignment.

Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>