mmc: sdhci-sprd: fixed incorrect clock divider

The register SDHCI_CLOCK_CONTROL should be cleared before config clock
divider, otherwise the frequency configured maybe lower than we
expected.

Fixes: fb8bd90f83 ("mmc: sdhci-sprd: Add Spreadtrum's initial host controller")
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Signed-off-by: Chunyan Zhang <zhang.lyra@gmail.com>
Reviewed-by: Baolin Wang <baolin.wang@linaro.org>
Tested-by: Baolin Wang <baolin.wang@linaro.org>
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sdhci-sprd.c

@@ -217,10 +217,11 @@ static inline void _sdhci_sprd_set_clock(struct sdhci_host *host,
 	struct sdhci_sprd_host *sprd_host = TO_SPRD_HOST(host);
 	u32 div, val, mask;
 
-	div = sdhci_sprd_calc_div(sprd_host->base_rate, clk);
+	sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
 
-	clk |= ((div & 0x300) >> 2) | ((div & 0xFF) << 8);
-	sdhci_enable_clk(host, clk);
+	div = sdhci_sprd_calc_div(sprd_host->base_rate, clk);
+	div = ((div & 0x300) >> 2) | ((div & 0xFF) << 8);
+	sdhci_enable_clk(host, div);
 
 	/* enable auto gate sdhc_enable_auto_gate */
 	val = sdhci_readl(host, SDHCI_SPRD_REG_32_BUSY_POSI);