[S390] keyboard: integer underflow bug

The "ct" variable should be an unsigned int.  Both struct kbdiacrs
->kb_cnt and struct kbd_data ->accent_table_size are unsigned ints.

Making it signed causes a problem in KBDIACRUC because the user could
set the signed bit and cause a buffer overflow.

Cc: <stable@kernel.org>
Signed-off-by: NDan Carpenter <error27@gmail.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/char/keyboard.c

@@ -460,7 +460,8 @@ kbd_ioctl(struct kbd_data *kbd, struct file *file,
 	  unsigned int cmd, unsigned long arg)
 {
 	void __user *argp;
-	int ct, perm;
+	unsigned int ct;
+	int perm;
 
 	argp = (void __user *)arg;