Input: ads7846 - strict_strtoul takes unsigned long

Fix sparse warning introduced by:
commit 160f1fef Input: convert drivers to use strict_strtoul()
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/touchscreen/ads7846.c

@@ -472,7 +472,7 @@ static ssize_t ads7846_disable_store(struct device *dev,
 				     const char *buf, size_t count)
 {
 	struct ads7846 *ts = dev_get_drvdata(dev);
-	long i;
+	unsigned long i;
 
 	if (strict_strtoul(buf, 10, &i))
 		return -EINVAL;