usb: dwc3: gadget: Fix request completion check

A request may not be completed because not all the TRBs are prepared for
it. This happens when we run out of available TRBs. When some TRBs are
completed, the driver needs to prepare the rest of the TRBs for the
request. The check dwc3_gadget_ep_request_completed() shouldn't be
checking the amount of data received but rather the number of pending
TRBs. Revise this request completion check.

Cc: stable@vger.kernel.org
Fixes: e0c42ce5

 ("usb: dwc3: gadget: simplify IOC handling")
Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>