hso modem detect fix patch against Alan Cox'es tty tree

Fixed incorrect check for the modem port, this prevents
crashes caused by issueing a tiocmget_submit_urb
on endpoints which don't exist for non modem devices.

Signed-off-by: Denis Joseph Barrow <D.Barow@option.com>
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>