memblock: fix missing comment of memblock_insert_region()

There is no comment for parameter nid of memblock_insert_region().
This patch adds comment for it.
Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memblock.c

@@ -326,6 +326,7 @@ static void __init_memblock memblock_merge_regions(struct memblock_type *type)
  * @idx:	index for the insertion point
  * @base:	base address of the new region
  * @size:	size of the new region
+ * @nid:	node id of the new region
  *
  * Insert new memblock region [@base,@base+@size) into @type at @idx.
  * @type must already have extra room to accomodate the new region.