bcachefs: Fix nocow write path closure bug

With regular waitlists, we need to ensure we always call finish_wait().
With closures, the equivalent is that we need to call closure_sync()
before returning with a stack-allocated closure.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/io.c

@@ -453,13 +453,13 @@ int bch2_extent_fallocate(struct btree_trans *trans,
 				opts.data_replicas,
 				opts.data_replicas,
 				RESERVE_none, 0, &cl, &wp);
-		if (bch2_err_matches(ret, BCH_ERR_operation_blocked)) {
+		if (ret) {
 			bch2_trans_unlock(trans);
 			closure_sync(&cl);
-			goto retry;
-		}
-		if (ret)
+			if (bch2_err_matches(ret, BCH_ERR_operation_blocked))
+				goto retry;
 			return ret;
+		}
 
 		sectors = min(sectors, wp->sectors_free);
 		sectors_allocated = sectors;