usb : gadget : fsl: fix the fault issue on rmmod

completion in udc_controller->done should be assign with proper
value before complete called. The complete called in fsl_udc_release
which intern called from usb_del_gadget_udc, so moving assignment
before calling usb_del_gadget_udc

Signed-off-by: Suresh Gupta <suresh.gupta@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>