USB: serial: io_edgeport: fix memory leaks in probe error path

URBs and buffers allocated in attach for Epic devices would never be
deallocated in case of a later probe error (e.g. failure to allocate
minor numbers) as disconnect is then never called.

Fix by moving deallocation to release and making sure that the
URBs are first unlinked.

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>