mmc: sdhci: get voltage from sdhc host

We use host->ocr_mask to hold the voltage get from device-tree
node, In case host->ocr_mask was available, we use host->ocr_mask
as the final available voltage can be used by MMC/SD/SDIO card.

Signed-off-by: Haijun Zhang <haijun.zhang@freescale.com>
Reviewed-by: Anton Vorontsov <anton@enomsg.org>
Signed-off-by: Chris Ball <cjb@laptop.org>