serial: 8250_early: fix comparison of different types

Fix the following sparse warning:

drivers/tty/serial/8250/8250_early.c:196:26: error: incompatible types in comparison expression (different type sizes)
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_early.c

@@ -194,7 +194,7 @@ static int __init parse_options(struct early_serial8250_device *device,
 		options++;
 		device->baud = simple_strtoul(options, NULL, 0);
 		length = min(strcspn(options, " ") + 1,
-			     sizeof(device->options));
+			     (size_t)(sizeof(device->options)));
 		strlcpy(device->options, options, length);
 	} else {
 		device->baud = probe_baud(port);