usb: gadget: net2280: Fix invalid handling of Reset irq

Without this patch, some hosts keep restarting indefinitely the target.

Fixes: ae8e530a (usb: gadget: net2280: Code Cleanup)
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>