mmc: sdhci: enable tuning for DDR50

CMD19 tuning is also available for DDR50 mode.
Signed-off-by: NWeijun Yang <york.yang@csr.com>
Signed-off-by: NBarry Song <Baohua.Song@csr.com>
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sdhci.c

@@ -1895,9 +1895,9 @@ static int sdhci_execute_tuning(struct mmc_host *mmc, u32 opcode)
 		tuning_count = host->tuning_count;
 
 	/*
-	 * The Host Controller needs tuning only in case of SDR104 mode
-	 * and for SDR50 mode when Use Tuning for SDR50 is set in the
-	 * Capabilities register.
+	 * The Host Controller needs tuning in case of SDR104 and DDR50
+	 * mode, and for SDR50 mode when Use Tuning for SDR50 is set in
+	 * the Capabilities register.
 	 * If the Host Controller supports the HS200 mode then the
 	 * tuning function has to be executed.
 	 */
@@ -1917,6 +1917,7 @@ static int sdhci_execute_tuning(struct mmc_host *mmc, u32 opcode)
 		break;
 
 	case MMC_TIMING_UHS_SDR104:
+	case MMC_TIMING_UHS_DDR50:
 		break;
 
 	case MMC_TIMING_UHS_SDR50: