usb: gadget: mv_udc: fix compile warning

| drivers/usb/gadget/mv_udc_core.c: In function 'handle_setup_packet':
| drivers/usb/gadget/mv_udc_core.c:1556:6: warning: 'status' may be \
	used uninitialized in this function

Signed-off-by: Felipe Balbi <balbi@ti.com>