mm/slub.c: remove a redundant assignment in ___slab_alloc()

When the code comes to this point, there are two cases:
1. cpu_slab is deactivated
2. cpu_slab is empty

In both cased, cpu_slab->freelist is NULL at this moment.

This patch removes the redundant assignment of cpu_slab->freelist.

Link: http://lkml.kernel.org/r/20170507031215.3130-1-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slub.c

@@ -2572,7 +2572,6 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 		page = c->page = c->partial;
 		c->partial = page->next;
 		stat(s, CPU_PARTIAL_ALLOC);
-		c->freelist = NULL;
 		goto redo;
 	}