mmc: sdhci-sprd: add get_ro hook function

sprd's sd host controller doesn't support write protect to sd card.

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

@@ -374,6 +374,11 @@ static unsigned int sdhci_sprd_get_max_timeout_count(struct sdhci_host *host)
 	return 1 << 31;
 }
 
+static unsigned int sdhci_sprd_get_ro(struct sdhci_host *host)
+{
+	return 0;
+}
+
 static struct sdhci_ops sdhci_sprd_ops = {
 	.read_l = sdhci_sprd_readl,
 	.write_l = sdhci_sprd_writel,
@@ -386,6 +391,7 @@ static struct sdhci_ops sdhci_sprd_ops = {
 	.set_uhs_signaling = sdhci_sprd_set_uhs_signaling,
 	.hw_reset = sdhci_sprd_hw_reset,
 	.get_max_timeout_count = sdhci_sprd_get_max_timeout_count,
+	.get_ro = sdhci_sprd_get_ro,
 };
 
 static void sdhci_sprd_request(struct mmc_host *mmc, struct mmc_request *mrq)