UPSTREAM: usb: dwc3: gadget: Initialize the TRB ring

UPSTREAM: usb: dwc3: gadget: Initialize the TRB ring

Clears out all the TRBs in the ring to clean up any stale data that
might be in them from the previous time the endpoint was enabled.

Also removed the existing clear of the LINK trb since the entire ring is
cleard just before.

Change-Id: I311d0931dc9daa6b6f6e39d252e54c37c516c190
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 0d25744ad107b6c9010153f3ebf8b59672b5b8e7)