serial: Use B0 instead of implicit zero assumption

Compare against B0 rather than assume B0 equals zero, which is true for
all archs but explicit B0 makes the code more obvious.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20230309080923.11778-3-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_core.c

@@ -1662,10 +1662,10 @@ static void uart_set_termios(struct tty_struct *tty,
 	cflag = tty->termios.c_cflag;
 
 	/* Handle transition to B0 status */
-	if ((old_termios->c_cflag & CBAUD) && !(cflag & CBAUD))
+	if (((old_termios->c_cflag & CBAUD) != B0) && ((cflag & CBAUD) == B0))
 		uart_clear_mctrl(uport, TIOCM_RTS | TIOCM_DTR);
 	/* Handle transition away from B0 status */
-	else if (!(old_termios->c_cflag & CBAUD) && (cflag & CBAUD)) {
+	else if (((old_termios->c_cflag & CBAUD) == B0) && ((cflag & CBAUD) != B0)) {
 		unsigned int mask = TIOCM_DTR;
 
 		if (!(cflag & CRTSCTS) || !tty_throttled(tty))