USB: serial: io_edgeport: fix memory leak in edge_startup

sysbot found memory leak in edge_startup().
The problem was that when an error was received from the usb_submit_urb(),
nothing was cleaned up.

Reported-by:  <syzbot+59f777bdcbdd7eea5305@syzkaller.appspotmail.com>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Fixes: 6e8cf775 ("USB: add EPIC support to the io_edgeport driver")
Cc: stable@vger.kernel.org	# 2.6.21: c5c0c555
Signed-off-by: Johan Hovold <johan@kernel.org>