staging: comedi: serial2002: use proper errno

checkpatch.pl reports:
WARNING: ENOSYS means 'invalid syscall nr' and nothing else

Change the error code to -ENOTTY.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/serial2002.c

@@ -101,7 +101,7 @@ static long serial2002_tty_ioctl(struct file *f, unsigned op,
 	if (f->f_op->unlocked_ioctl)
 		return f->f_op->unlocked_ioctl(f, op, param);
 
-	return -ENOSYS;
+	return -ENOTTY;
 }
 
 static int serial2002_tty_write(struct file *f, unsigned char *buf, int count)