bcachefs: Fix -Wc23-extensions in bch2_check_dirents()

Clang warns (or errors with CONFIG_WERROR=y):

  fs/bcachefs/fsck.c:2325:2: error: label followed by a declaration is a C23 extension [-Werror,-Wc23-extensions]
   2325 |         int ret = bch2_trans_run(c,
        |         ^

On clang-17 and older, this is an unconditional error:

  fs/bcachefs/fsck.c:2325:2: error: expected expression
   2325 |         int ret = bch2_trans_run(c,
        |         ^

Move the declaration of ret to the top of the function to resolve both
ways this issue manifests.

Fixes: c72def5 ("bcachefs: Run check_dirents second time if required")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Author: nathanchance

fs/bcachefs/fsck.c

@@ -2313,10 +2313,11 @@ int bch2_check_dirents(struct bch_fs *c)
 	struct snapshots_seen s;
 	struct bch_hash_info hash_info;
 	bool need_second_pass = false, did_second_pass = false;
+	int ret;
 
 	snapshots_seen_init(&s);
 again:
-	int ret = bch2_trans_run(c,
+	ret = bch2_trans_run(c,
 		for_each_btree_key_commit(trans, iter, BTREE_ID_dirents,
 				POS(BCACHEFS_ROOT_INO, 0),
 				BTREE_ITER_prefetch|BTREE_ITER_all_snapshots, k,