ext4: make the IS_EXT2_SB/IS_EXT3_SB checks more robust

Check for sb->s_type which is the right place to look at the file system
type, not the holder, which is just an implementation detail in the VFS
helpers.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Message-Id: <20230802154131.2221419-6-hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/ext4/super.c

@@ -141,7 +141,7 @@ static struct file_system_type ext2_fs_type = {
 };
 MODULE_ALIAS_FS("ext2");
 MODULE_ALIAS("ext2");
-#define IS_EXT2_SB(sb) ((sb)->s_bdev->bd_holder == &ext2_fs_type)
+#define IS_EXT2_SB(sb) ((sb)->s_type == &ext2_fs_type)
 #else
 #define IS_EXT2_SB(sb) (0)
 #endif
@@ -157,7 +157,7 @@ static struct file_system_type ext3_fs_type = {
 };
 MODULE_ALIAS_FS("ext3");
 MODULE_ALIAS("ext3");
-#define IS_EXT3_SB(sb) ((sb)->s_bdev->bd_holder == &ext3_fs_type)
+#define IS_EXT3_SB(sb) ((sb)->s_type == &ext3_fs_type)
 
 
 static inline void __ext4_read_bh(struct buffer_head *bh, blk_opf_t op_flags,