atmel-mci: fix sdc_reg typo

This fixes a bug when setting the sdc_reg for 4-bit bus width
transactions.

Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

drivers/mmc/host/atmel-mci.c

@@ -812,7 +812,7 @@ static void atmci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 		slot->sdc_reg |= MCI_SDCBUS_1BIT;
 		break;
 	case MMC_BUS_WIDTH_4:
-		slot->sdc_reg = MCI_SDCBUS_4BIT;
+		slot->sdc_reg |= MCI_SDCBUS_4BIT;
 		break;
 	}