TTY: quatech2, remove unneeded is_open

tty->ops->break_ctl cannot be called outside the gap between open and
close. So there is no need to check whether the port is open in
break_ctl in quatech2. Remove the check and also that member
completely.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Bill Pemberton <wfp5p@virginia.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>