board: imx6dl-sielaff: spl.c: Remove multiline string

Remove the malformed multiline string and fix the checkpatch warning.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>

board/sielaff/imx6dl-sielaff/spl.c

@@ -93,8 +93,8 @@ int board_mmc_init(struct bd_info *bis)
 			usdhc_cfg[0].sdhc_clk = mxc_get_clock(MXC_ESDHC3_CLK);
 			break;
 		default:
-			printf("Warning: you configured more USDHC controllers \
-				(%d) than supported by the board\n", i + 1);
+			printf("Warning: you configured more USDHC controllers (%d) than supported by the board\n",
+			       i + 1);
 			return -EINVAL;
 		}