mmc: sdhci-s3c: initialize host->quirks2 for using quirks2

In order to use the quirks2, initialized the host->quirks2.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Kyungmin Park <Kyungmin.park@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>