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

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>