mmc: dwmmc: return a proper error code when busy

When failing to send a command because the hardware is busy, return
EBUSY to indicate the cause instead of just -1.

Signed-off-by: John Keeping <john@metanate.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/drivers/mmc/dw_mmc.c b/drivers/mmc/dw_mmc.c
index a949dad..4232c5e 100644
--- a/drivers/mmc/dw_mmc.c
+++ b/drivers/mmc/dw_mmc.c
@@ -301,7 +301,7 @@
 		flags = dwmci_set_transfer_mode(host, data);
 
 	if ((cmd->resp_type & MMC_RSP_136) && (cmd->resp_type & MMC_RSP_BUSY))
-		return -1;
+		return -EBUSY;
 
 	if (cmd->cmdidx == MMC_CMD_STOP_TRANSMISSION)
 		flags |= DWMCI_CMD_ABORT_STOP;