mmc: dwmmc: Change designware MMC 'clksel' callback function to return status

Change 'clksel' callback function to allow the code to return a
status.

This patch is a preparation for enabling Arm-Trusted-Firmware (ATF)
in Intel SoC FPGA. This patch does not change functionality.

When using Arm-Trusted-Firmware (ATF) in Intel SoC FPGA, the MMC clock
related register is secure register which is required to be written
via SMC/PCSI call. It is possible that U-Boot fail to write the
register if there is unexpected error between U-Boot and ATF.
As a result, there maybe signal integrity on MMC connection due to
clock. So, the code should reports error to user when 'clksel' fail.

Signed-off-by: Siew Chin Lim <elly.siew.chin.lim@intel.com>
diff --git a/drivers/mmc/exynos_dw_mmc.c b/drivers/mmc/exynos_dw_mmc.c
index 3aa9fb3..2fc1ef1 100644
--- a/drivers/mmc/exynos_dw_mmc.c
+++ b/drivers/mmc/exynos_dw_mmc.c
@@ -44,7 +44,7 @@
  * Function used as callback function to initialise the
  * CLKSEL register for every mmc channel.
  */
-static void exynos_dwmci_clksel(struct dwmci_host *host)
+static int exynos_dwmci_clksel(struct dwmci_host *host)
 {
 #ifdef CONFIG_DM_MMC
 	struct dwmci_exynos_priv_data *priv =
@@ -53,6 +53,8 @@
 	struct dwmci_exynos_priv_data *priv = host->priv;
 #endif
 	dwmci_writel(host, DWMCI_CLKSEL, priv->sdr_timing);
+
+	return 0;
 }
 
 unsigned int exynos_dwmci_get_clk(struct dwmci_host *host, uint freq)