serial: 8250: fix return error code in serial8250_request_std_resource()

serial: 8250: fix return error code in serial8250_request_std_resource()

If port->mapbase = NULL in serial8250_request_std_resource() , it need
return a error code instead of 0. If uart_set_info() fail to request new
regions by serial8250_request_std_resource() but the return value of
serial8250_request_std_resource() is 0, The system incorrectly considers
that the resource application is successful and does not attempt to
restore the old setting. A null pointer reference is triggered when the
port resource is later invoked.

Signed-off-by: Yi Yang <yiyang13@huawei.com>
Cc: stable <stable@kernel.org>
Link: https://lore.kernel.org/r/20220628083515.64138-1-yiyang13@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>