bcachefs: allocate inode by using alloc_inode_sb()

The inode allocation is supposed to use alloc_inode_sb(), so convert
kmem_cache_alloc() to alloc_inode_sb().

It will also fix [1] to avoid the NULL pointer dereference BUG in
list_lru_add() when CONFIG_MEMCG is enabled.

Links:
[1]: https://lore.kernel.org/all/20589721-46c0-4344-b2ef-6ab48bbe2ea5@linux.dev/
[2]: https://lore.kernel.org/all/7db60e36-9c96-4938-a28d-a9745e287386@linux.dev/

Fixes: 86d81ec5 ("bcachefs: Mark bch_inode_info as SLAB_ACCOUNT")
Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/fs.c

@@ -293,7 +293,8 @@ static struct inode *bch2_alloc_inode(struct super_block *sb)
 
 static struct bch_inode_info *__bch2_new_inode(struct bch_fs *c)
 {
-	struct bch_inode_info *inode = kmem_cache_alloc(bch2_inode_cache, GFP_NOFS);
+	struct bch_inode_info *inode = alloc_inode_sb(c->vfs_sb,
+						bch2_inode_cache, GFP_NOFS);
 	if (!inode)
 		return NULL;