slab: simplify init_kmem_cache_nodes() error handling

We don't need to call free_kmem_cache_nodes() immediately when failing
to allocate a kmem_cache_node, because when we return 0,
do_kmem_cache_create() calls __kmem_cache_release() which also performs
free_kmem_cache_nodes().

Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>