usb: dwc3: gadget: Clear pending events when stopping controller

After clearing run/stop bit there might be events still pending
with the controller which will not allow the controller to be
halted. Fix this by simply clearing GEVNTCOUNT(n) by reading and
writing back the counts.

Change-Id: Id93df8effe73b1765cced65590679b7df6c232da
Signed-off-by: Pratham Pratap <prathampratap@codeaurora.org>