tty: 8250/serial_cs, propagate errors in simple_config

The caller expects from the others (pfc_config and multi_config) to
return standard error values. So do the same for simple_config too.

We invert the if condition to handle the error case.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210302062214.29627-13-jslaby@suse.cz


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