mmc: dw_mmc: fix misleading error print if failing to do DMA transfer

The original log didn't figure out that we could still
finish this transfer by PIO mode even if failing to use
DMA. And it should be kept for debug level instead of
error one.
Signed-off-by: NShawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: NJaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/dw_mmc.c

@@ -1057,8 +1057,10 @@ static int dw_mci_submit_data_dma(struct dw_mci *host, struct mmc_data *data)
 	spin_unlock_irqrestore(&host->irq_lock, irqflags);
 
 	if (host->dma_ops->start(host, sg_len)) {
-		/* We can't do DMA */
-		dev_err(host->dev, "%s: failed to start DMA.\n", __func__);
+		/* We can't do DMA, try PIO for this one */
+		dev_dbg(host->dev,
+			"%s: fall back to PIO mode for current transfer\n",
+			__func__);
 		return -ENODEV;
 	}