usb: dwc3: ep0: fix GetStatus handling (again)

previous commit fixed part of it but it was still
calling usb_ep_queue() from IRQ context without
loosing locks. That cannot be done otherwise we will
have a recursive locking.

Also, we need to assign the 'dep' pointer on
dwc->ep0_usb_req otherwise we will have a NULL
pointer dereference on dwc3_map_buffer_to_dma().

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