tty: serial: samsung: fix tx_empty() to return TIOCSER_TEMT

The core expects for tx_empty() either TIOCSER_TEMT when the tx is
empty or 0 otherwise. s3c24xx_serial_txempty_nofifo() might return
0x4, and at least uart_get_lsr_info() tries to clear exactly
TIOCSER_TEMT (BIT(1)). Fix tx_empty() to return TIOCSER_TEMT.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Link: https://lore.kernel.org/r/20240119104526.1221243-2-tudor.ambarus@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/samsung_tty.c

@@ -987,11 +987,10 @@ static unsigned int s3c24xx_serial_tx_empty(struct uart_port *port)
 		if ((ufstat & info->tx_fifomask) != 0 ||
 		    (ufstat & info->tx_fifofull))
 			return 0;
-
-		return 1;
+		return TIOCSER_TEMT;
 	}
 
-	return s3c24xx_serial_txempty_nofifo(port);
+	return s3c24xx_serial_txempty_nofifo(port) ? TIOCSER_TEMT : 0;
 }
 
 /* no modem control lines */