tty: rework break handling

Some hardware needs to do break handling itself and may have partial
support only. Make break_ctl return an error code. Add a tty driver flag
so you can indicate driver hardware side break support.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/char/sx.c b/drivers/char/sx.c
index d5cffcd..2162439b 100644
--- a/drivers/char/sx.c
+++ b/drivers/char/sx.c
@@ -1840,7 +1840,7 @@
 	return rc;
 }
 
-static void sx_break(struct tty_struct *tty, int flag)
+static int sx_break(struct tty_struct *tty, int flag)
 {
 	struct sx_port *port = tty->driver_data;
 	int rv;
@@ -1857,6 +1857,7 @@
 			read_sx_byte(port->board, CHAN_OFFSET(port, hi_hstat)));
 	unlock_kernel();
 	func_exit();
+	return 0;
 }
 
 static int sx_tiocmget(struct tty_struct *tty, struct file *file)