tty: n_tty: make flow of n_tty_receive_buf_common() a bool

The 'flow' parameter of n_tty_receive_buf_common() is meant to be a
boolean value. So use bool and alter call sites accordingly.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20230827074147.2287-2-jirislaby@kernel.org


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