mmc: sdhci-of-esdhc: avoid writing power control register

The eSDHC doesn't have a standard power control register, so when
writing this register in stack we should do nothing to avoid
incorrect operation.
Signed-off-by: NYangbo Lu <yangbo.lu@freescale.com>
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sdhci-of-esdhc.c

@@ -182,6 +182,12 @@ static u32 esdhc_writeb_fixup(struct sdhci_host *host,
 	u8 tmp;
 	int shift = (spec_reg & 0x3) * 8;
 
+	/*
+	 * eSDHC doesn't have a standard power control register, so we do
+	 * nothing here to avoid incorrect operation.
+	 */
+	if (spec_reg == SDHCI_POWER_CONTROL)
+		return old_value;
 	/*
 	 * "DMA select" location is offset 0x28 in SD specification, but on
 	 * P5020 or P3041, it's located at 0x29.