btrfs: move folio initialization to one place in attach_eb_folio_to_filemap()

This is just a trivial change. The code looks a bit more readable this way, IMO.

Move initialization of existing_folio to the beginning of the retry loop
so it's set to NULL at one place.

Signed-off-by: Daniel Vacek <neelx@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: Daniel Vacek

fs/btrfs/extent_io.c

@@ -3107,7 +3107,7 @@ static int attach_eb_folio_to_filemap(struct extent_buffer *eb, int i,
 	struct btrfs_fs_info *fs_info = eb->fs_info;
 	struct address_space *mapping = fs_info->btree_inode->i_mapping;
 	const unsigned long index = eb->start >> PAGE_SHIFT;
-	struct folio *existing_folio = NULL;
+	struct folio *existing_folio;
 	int ret;
 
 	ASSERT(found_eb_ret);
@@ -3116,17 +3116,16 @@ static int attach_eb_folio_to_filemap(struct extent_buffer *eb, int i,
 	ASSERT(eb->folios[i]);
 
 retry:
+	existing_folio = NULL;
 	ret = filemap_add_folio(mapping, eb->folios[i], index + i,
 				GFP_NOFS | __GFP_NOFAIL);
 	if (!ret)
 		goto finish;
 
 	existing_folio = filemap_lock_folio(mapping, index + i);
 	/* The page cache only exists for a very short time, just retry. */
-	if (IS_ERR(existing_folio)) {
-		existing_folio = NULL;
+	if (IS_ERR(existing_folio))
 		goto retry;
-	}
 
 	/* For now, we should only have single-page folios for btree inode. */
 	ASSERT(folio_nr_pages(existing_folio) == 1);