mmc: sdhci: add support for realtek rts5250

Add support for realtek rts5250 pci card reader. The card reader has
some problems with DDR50 mode, so add a new quirks2 for broken ddr50.

Signed-off-by: Micky Ching <micky_ching@realsil.com.cn>
Signed-off-by: Chris Ball <chris@printf.net>
diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 9ddef47..8958edc 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -3020,7 +3020,8 @@
 	} else if (caps[1] & SDHCI_SUPPORT_SDR50)
 		mmc->caps |= MMC_CAP_UHS_SDR50;
 
-	if (caps[1] & SDHCI_SUPPORT_DDR50)
+	if ((caps[1] & SDHCI_SUPPORT_DDR50) &&
+		!(host->quirks2 & SDHCI_QUIRK2_BROKEN_DDR50))
 		mmc->caps |= MMC_CAP_UHS_DDR50;
 
 	/* Does the host need tuning for SDR50? */