usb: gadget: gadgetfs: use after free in dev_release()

The call to put_dev() releases "dev".  Hopefully, we don't need to set
the state to STATE_DEV_DISABLED anyway so I have removed those lines.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>