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/ca_dw_mmc.c b/drivers/mmc/ca_dw_mmc.c
index fad2ff5..2b79356 100644
--- a/drivers/mmc/ca_dw_mmc.c
+++ b/drivers/mmc/ca_dw_mmc.c
@@ -40,7 +40,7 @@
 	u8 ds;
 };
 
-static void ca_dwmci_clksel(struct dwmci_host *host)
+static int ca_dwmci_clksel(struct dwmci_host *host)
 {
 	struct ca_dwmmc_priv_data *priv = host->priv;
 	u32 val = readl(priv->sd_dll_reg);
@@ -52,6 +52,8 @@
 		val |= SD_CLK_SEL_100MHZ;
 
 	writel(val, priv->sd_dll_reg);
+
+	return 0;
 }
 
 static void ca_dwmci_board_init(struct dwmci_host *host)