usb: dwc: dbm: save resource index during enqueue

The DWC3 maintains a number of each enqueued TRB
at the time it is queued. This number must be
referenced when dequeuing (or performing other
operations on) the TRB. This patch saves the resource
number for cases where the DBM is used to interface
the DWC.

Change-Id: Ibe19a0e6df97487c6f133ebd3f3e2dceeb9e534d
Signed-off-by: Bar Weiner <bweiner@codeaurora.org>