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

Private data, URBs and buffers allocated for Epic devices during
attach were never released on errors (e.g. missing endpoints).

Fixes: 6e8cf775 ("USB: add EPIC support to the io_edgeport driver")
Cc: stable <stable@vger.kernel.org>	# v2.6.21
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>