mmc: dw_mmc: fixed the wrong bit control

If mode is not DDR-mode, then it needs to clear it.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/drivers/mmc/dw_mmc.c b/drivers/mmc/dw_mmc.c
index b18c75d..76fa0b0 100644
--- a/drivers/mmc/dw_mmc.c
+++ b/drivers/mmc/dw_mmc.c
@@ -321,7 +321,7 @@
 	if (mmc->ddr_mode)
 		regs |= DWMCI_DDR_MODE;
 	else
-		regs &= DWMCI_DDR_MODE;
+		regs &= ~DWMCI_DDR_MODE;
 
 	dwmci_writel(host, DWMCI_UHS_REG, regs);