io_uring: provide io_resubmit_prep() stub for !CONFIG_BLOCK

Randy reports the following error on CONFIG_BLOCK not being set:

../fs/io_uring.c: In function ‘kiocb_done’:
../fs/io_uring.c:2766:7: error: implicit declaration of function ‘io_resubmit_prep’; did you mean ‘io_put_req’? [-Werror=implicit-function-declaration]
   if (io_resubmit_prep(req)) {

Provide a dummy stub for io_resubmit_prep() like we do for
io_rw_should_reissue(), which also helps remove an ifdef sequence from
io_complete_rw_iopoll() as well.

Fixes: 8c130827f4 ("io_uring: don't alter iopoll reissue fail ret code")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -2464,6 +2464,10 @@ static bool io_rw_should_reissue(struct io_kiocb *req)
 	return true;
 }
 #else
+static bool io_resubmit_prep(struct io_kiocb *req)
+{
+	return false;
+}
 static bool io_rw_should_reissue(struct io_kiocb *req)
 {
 	return false;
@@ -2504,14 +2508,8 @@ static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
 	if (kiocb->ki_flags & IOCB_WRITE)
 		kiocb_end_write(req);
 	if (unlikely(res != req->result)) {
-		bool fail = true;
-
-#ifdef CONFIG_BLOCK
-		if (res == -EAGAIN && io_rw_should_reissue(req) &&
-		    io_resubmit_prep(req))
-			fail = false;
-#endif
-		if (fail) {
+		if (!(res == -EAGAIN && io_rw_should_reissue(req) &&
+		    io_resubmit_prep(req))) {
 			req_set_fail_links(req);
 			req->flags |= REQ_F_DONT_REISSUE;
 		}