mm/slob.c: remove an unnecessary check for __GFP_ZERO

Current flow guarantees a valid pointer when handling the __GFP_ZERO
case.  So remove the unnecessary NULL pointer check.

Link: http://lkml.kernel.org/r/1507203141-11959-1-git-send-email-miles.chen@mediatek.com
Signed-off-by: Miles Chen <miles.chen@mediatek.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/slob.c

@@ -330,7 +330,7 @@ static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
 		BUG_ON(!b);
 		spin_unlock_irqrestore(&slob_lock, flags);
 	}
-	if (unlikely((gfp & __GFP_ZERO) && b))
+	if (unlikely(gfp & __GFP_ZERO))
 		memset(b, 0, size);
 	return b;
 }