USB: serial: keyspan: fix use-after-free in probe error path

The interface instat and indat URBs were submitted in attach, but never
unlinked in release before deallocating the corresponding transfer
buffers.

In the case of a late probe error (e.g. due to failed minor allocation),
disconnect would not have been called before release, causing the
buffers to be freed while the URBs are still in use. We'd also end up
with active URBs for an unbound interface.

Fixes: f9c99bb8 ("USB: usb-serial: replace shutdown with disconnect,
release")
Cc: stable <stable@vger.kernel.org>	# v2.6.31
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>