UPSTREAM: usb: dwc3: gadget: Handle TRB index 0 when full or empty

UPSTREAM: usb: dwc3: gadget: Handle TRB index 0 when full or empty

If the trb->enqueue == trb->dequeue, then it could be full or empty.
This could also happen at TRB index 0, so modify the check to handle
that condition. At index 0, the previous TRB is the one just before the
link TRB.

Change-Id: I17d5fd4e7592507dac08bef6c458ff14d7426461
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Wu Liang feng <wulf@rock-chips.com>
(cherry picked from commit 361572b5f7a95b341a92d34b9bf41f71bbdae34d)