ipwireless: remove unused ipw_tty::closing

It's only set, but never read because commit 01261cb9 ("tty:
ipwireless: Remove tty->closing abort from ipw_open()") removed last use
of tty::closing.

Cc: Jiri Kosina <jikos@kernel.org>
Cc: David Sterba <dsterba@suse.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210610090307.2689-1-jslaby@suse.cz


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