quota: Factor out setup of quota inode

[ Upstream commit c7d3d28360fdb3ed3a5aa0bab19315e0fdc994a1 ]

Factor out setting up of quota inode and eventual error cleanup from
vfs_load_quota_inode(). This will simplify situation for filesystems
that don't have any quota inodes.

Signed-off-by: Jan Kara <jack@suse.cz>
Stable-dep-of: d32387748476 ("ext4: fix bug_on in __es_tree_search caused by bad quota inode")
Signed-off-by: Sasha Levin <sashal@kernel.org>