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/mxser.c b/drivers/char/mxser.c
index 1fb2557..f04c3c5 100644
--- a/drivers/char/mxser.c
+++ b/drivers/char/mxser.c
@@ -2183,7 +2183,7 @@
 /*
  * mxser_rs_break() --- routine which turns the break handling on or off
  */
-static void mxser_rs_break(struct tty_struct *tty, int break_state)
+static int mxser_rs_break(struct tty_struct *tty, int break_state)
 {
 	struct mxser_port *info = tty->driver_data;
 	unsigned long flags;
@@ -2196,6 +2196,7 @@
 		outb(inb(info->ioaddr + UART_LCR) & ~UART_LCR_SBC,
 			info->ioaddr + UART_LCR);
 	spin_unlock_irqrestore(&info->slock, flags);
+	return 0;
 }
 
 static void mxser_receive_chars(struct mxser_port *port, int *status)