usb: cdnsp: Fixed issue with ZLP

The condition "if (need_zero_pkt && zero_len_trb)" was always false
and it caused that TRB for ZLP was not prepared.

Fix causes that after preparing last TRB in TD, the driver prepares
additional TD with ZLP when a ZLP is required.

Cc: <stable@vger.kernel.org>
Fixes: 3d82904559 ("usb: cdnsp: cdns3 Add main part of Cadence USBSSP DRD Driver")
Signed-off-by: Pawel Laszczak <pawell@cadence.com>
Link: https://lore.kernel.org/r/20210623072728.41275-1-pawell@gli-login.cadence.com
Signed-off-by: Peter Chen <peter.chen@kernel.org>

drivers/usb/cdns3/cdnsp-ring.c

@@ -1932,16 +1932,14 @@ int cdnsp_queue_bulk_tx(struct cdnsp_device *pdev, struct cdnsp_request *preq)
 		}
 
 		if (enqd_len + trb_buff_len >= full_len) {
-			if (need_zero_pkt && zero_len_trb) {
-				zero_len_trb = true;
-			} else {
+			if (need_zero_pkt)
+				zero_len_trb = !zero_len_trb;
+
 			field &= ~TRB_CHAIN;
 			field |= TRB_IOC;
 			more_trbs_coming = false;
-				need_zero_pkt = false;
 			preq->td.last_trb = ring->enqueue;
 		}
-		}
 
 		/* Only set interrupt on short packet for OUT endpoints. */
 		if (!preq->direction)
@@ -1955,7 +1953,7 @@ int cdnsp_queue_bulk_tx(struct cdnsp_device *pdev, struct cdnsp_request *preq)
 		length_field = TRB_LEN(trb_buff_len) | TRB_TD_SIZE(remainder) |
 			TRB_INTR_TARGET(0);
 
-		cdnsp_queue_trb(pdev, ring, more_trbs_coming | need_zero_pkt,
+		cdnsp_queue_trb(pdev, ring, more_trbs_coming | zero_len_trb,
 				lower_32_bits(send_addr),
 				upper_32_bits(send_addr),
 				length_field,