Input: fix signedness warning in input_set_keycode()

The dev->getkeycode() method expects unsigned argument.
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/input.c

@@ -694,7 +694,7 @@ int input_set_keycode(struct input_dev *dev,
 		      unsigned int scancode, unsigned int keycode)
 {
 	unsigned long flags;
-	int old_keycode;
+	unsigned int old_keycode;
 	int retval;
 
 	if (keycode > KEY_MAX)