rsxx: remove redundant NULL check

Fix below warnings reported by coccicheck:
./drivers/block/rsxx/dma.c:948:3-8: WARNING: NULL check
before some freeing functions is not needed.
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <abaci-bugfix@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/rsxx/dma.c

@@ -944,8 +944,7 @@ int rsxx_dma_setup(struct rsxx_cardinfo *card)
 			ctrl->done_wq = NULL;
 		}
 
-		if (ctrl->trackers)
-			vfree(ctrl->trackers);
+		vfree(ctrl->trackers);
 
 		if (ctrl->status.buf)
 			dma_free_coherent(&card->dev->dev, STATUS_BUFFER_SIZE8,