tty/serial: 8250_exar: use true,false for bool variable

Fixes coccicheck warning:

drivers/tty/serial/8250/8250_exar.c:189:6-17: WARNING: Assignment of 0/1 to bool variable
drivers/tty/serial/8250/8250_exar.c:197:3-14: WARNING: Assignment of 0/1 to bool variable
drivers/tty/serial/8250/8250_exar.c:199:3-14: WARNING: Assignment of 0/1 to bool variable

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
Link: https://lore.kernel.org/r/1578881777-65475-5-git-send-email-zhengbin13@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_exar.c

@@ -186,7 +186,7 @@ static int xr17v35x_startup(struct uart_port *port)
 static void exar_shutdown(struct uart_port *port)
 {
 	unsigned char lsr;
-	bool tx_complete = 0;
+	bool tx_complete = false;
 	struct uart_8250_port *up = up_to_u8250p(port);
 	struct circ_buf *xmit = &port->state->xmit;
 	int i = 0;
@@ -194,9 +194,9 @@ static void exar_shutdown(struct uart_port *port)
 	do {
 		lsr = serial_in(up, UART_LSR);
 		if (lsr & (UART_LSR_TEMT | UART_LSR_THRE))
-			tx_complete = 1;
+			tx_complete = true;
 		else
-			tx_complete = 0;
+			tx_complete = false;
 		usleep_range(1000, 1100);
 	} while (!uart_circ_empty(xmit) && !tx_complete && i++ < 1000);