mm: multi-gen LRU: use macro for bitmap

Use DECLARE_BITMAP macro when possible.

Link: https://lkml.kernel.org/r/20230522112058.2965866-1-talumbau@google.com
Signed-off-by: T.J. Alumbaugh <talumbau@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yuanchu Xie <yuanchu@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vmscan.c

@@ -4144,7 +4144,7 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
 	unsigned long next;
 	unsigned long addr;
 	struct vm_area_struct *vma;
-	unsigned long bitmap[BITS_TO_LONGS(MIN_LRU_BATCH)];
+	DECLARE_BITMAP(bitmap, MIN_LRU_BATCH);
 	unsigned long first = -1;
 	struct lru_gen_mm_walk *walk = args->private;