Revert "serial_core: Update buffer overrun statistics."

This reverts commit 64218087.

Buffer overruns are for hardware reported overruns, not software ones,
which will only happen if we run out of memory and you will get lots of
-ENOMEM errors at the same time.

Thanks to Alan Cox for catching this.
Reported-by: Alan Cox <alan@linux.intel.com>
Cc: Corbin Atkinson <corbinat@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_core.c

@@ -2527,16 +2527,14 @@ void uart_insert_char(struct uart_port *port, unsigned int status,
 	struct tty_struct *tty = port->state->port.tty;
 
 	if ((status & port->ignore_status_mask & ~overrun) == 0)
-		if (tty_insert_flip_char(tty, ch, flag) == 0)
-			++port->icount.buf_overrun;
+		tty_insert_flip_char(tty, ch, flag);
 
 	/*
 	 * Overrun is special.  Since it's reported immediately,
 	 * it doesn't affect the current character.
 	 */
 	if (status & ~port->ignore_status_mask & overrun)
-		if (tty_insert_flip_char(tty, 0, TTY_OVERRUN) == 0)
-			++port->icount.buf_overrun;
+		tty_insert_flip_char(tty, 0, TTY_OVERRUN);
 }
 EXPORT_SYMBOL_GPL(uart_insert_char);