mm/slab.c: update outdated kmem_list3 in a comment

kmem_list3 has been renamed to kmem_cache_node long long ago so update it.

References:
6744f08 ("slab: Common name for the per node structures")
ce8eb6c ("slab: Rename list3/l3 to node")

Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Pekka Enberg <penberg@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Link: http://lkml.kernel.org/r/20200722033355.26908-1-yangx.jy@cn.fujitsu.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slab.c

@@ -1060,7 +1060,7 @@ int slab_prepare_cpu(unsigned int cpu)
  * offline.
  *
  * Even if all the cpus of a node are down, we don't free the
- * kmem_list3 of any cache. This to avoid a race between cpu_down, and
+ * kmem_cache_node of any cache. This to avoid a race between cpu_down, and
  * a kmalloc allocation from another cpu for memory from the node of
  * the cpu going down.  The list3 structure is usually allocated from
  * kmem_cache_create() and gets destroyed at kmem_cache_destroy().