net: asix: Avoid looping when the device is disconnected

From: Vincent Palatin <vpalatin@chromium.org>

Check the answers from the USB stack and avoid re-sending multiple times
the request if the device has disappeared.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
Signed-off-by: Robert Foss <robert.foss@collabora.com>
Tested-by: Robert Foss <robert.foss@collabora.com>
Signed-off-by: David S. Miller <davem@davemloft.net>