serial: ns16550: Fix style violation

Clarify the computation precedence in two ternary operator
constructions.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Mario Six <mario.six@gdsys.cc>

drivers/serial/ns16550.c

@@ -339,9 +339,9 @@ static int ns16550_serial_pending(struct udevice *dev, bool input)
 	struct NS16550 *const com_port = dev_get_priv(dev);
 
 	if (input)
-		return serial_in(&com_port->lsr) & UART_LSR_DR ? 1 : 0;
+		return (serial_in(&com_port->lsr) & UART_LSR_DR) ? 1 : 0;
 	else
-		return serial_in(&com_port->lsr) & UART_LSR_THRE ? 0 : 1;
+		return (serial_in(&com_port->lsr) & UART_LSR_THRE) ? 0 : 1;
 }
 
 static int ns16550_serial_getc(struct udevice *dev)