io_uring: correct __must_hold annotation

io_req_free_batch() has a __must_hold annotation referencing a
request being passed in, but we're passing in the context.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -2182,7 +2182,7 @@ static void io_req_free_batch(struct req_batch *rb, struct io_kiocb *req,
 }
 
 static void io_submit_flush_completions(struct io_ring_ctx *ctx)
-	__must_hold(&req->ctx->uring_lock)
+	__must_hold(&ctx->uring_lock)
 {
 	struct io_submit_state *state = &ctx->submit_state;
 	int i, nr = state->compl_nr;