sandbox: spi: Add newline to printf() in sandbox_sf_probe

This printf() should have a newline at the end. Add it.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>

drivers/mtd/spi/sandbox.c

@@ -129,7 +129,7 @@ static int sandbox_sf_probe(struct udevice *dev)
 		}
 	}
 	if (cs == -1) {
-		printf("Error: Unknown chip select for device '%s'",
+		printf("Error: Unknown chip select for device '%s'\n",
 		       dev->name);
 		return -EINVAL;
 	}