tty: serial: linflexuart: Remove redundant check to simplify the code

In the function uart_add_one_port(), it can return zero or non-zero,
so remove redundant check to simplify the code.

Signed-off-by: Zhang Shengju <zhangshengju@cmss.chinamobile.com>
Signed-off-by: Tang Bin <tangbin@cmss.chinamobile.com>
Link: https://lore.kernel.org/r/20210823110754.11232-1-tangbin@cmss.chinamobile.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>