USB: iowarrior: fix use-after-free after driver unbind

USB: iowarrior: fix use-after-free after driver unbind

Make sure to stop also the asynchronous write URBs on disconnect() to
avoid use-after-free in the completion handler after driver unbind.

Fixes: 31278f37cb65 ("USB: add driver for iowarrior devices.")
Cc: stable <stable@vger.kernel.org>	# 2.6.21: 0110765354b0 ("USB: introduce usb_anchor")
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191009104846.5925-4-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>