mmc: sdhci: Remove unneeded quirk2 flag of O2 SD host controller

O2 SD host controller only need set the quirk2 flag
SDHCI_QUIRK2_CLEAR_TRANSFERMODE_REG_BEFORE_CMD when
work on force 1.8v emmc mode but not normal mode

Signed-off-by: Ernest Zhang <ernest.zhang@bayhubtech.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>