mmc: add support for write protection

Add generic mmc write protection functionality.

Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>
diff --git a/drivers/mmc/sh_mmcif.c b/drivers/mmc/sh_mmcif.c
index 4588568..011d4f3 100644
--- a/drivers/mmc/sh_mmcif.c
+++ b/drivers/mmc/sh_mmcif.c
@@ -599,6 +599,7 @@
 	mmc->set_ios = sh_mmcif_set_ios;
 	mmc->init = sh_mmcif_init;
 	mmc->getcd = NULL;
+	mmc->getwp = NULL;
 	host->regs = (struct sh_mmcif_regs *)CONFIG_SH_MMCIF_ADDR;
 	host->clk = CONFIG_SH_MMCIF_CLK;
 	mmc->priv = host;