bcache: clean up do_btree_node_write a bit

Use a variable containing the buffer address instead of the to be
removed integer iterator from bio_for_each_segment_all.
Suggested-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Acked-by: Coly Li <colyli@suse.de>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/bcache/btree.c

@@ -431,12 +431,13 @@ static void do_btree_node_write(struct btree *b)
 	if (!bch_bio_alloc_pages(b->bio, __GFP_NOWARN|GFP_NOWAIT)) {
 		int j;
 		struct bio_vec *bv;
-		void *base = (void *) ((unsigned long) i & ~(PAGE_SIZE - 1));
+		void *addr = (void *) ((unsigned long) i & ~(PAGE_SIZE - 1));
 		struct bvec_iter_all iter_all;
 
-		bio_for_each_segment_all(bv, b->bio, j, iter_all)
-			memcpy(page_address(bv->bv_page),
-			       base + j * PAGE_SIZE, PAGE_SIZE);
+		bio_for_each_segment_all(bv, b->bio, j, iter_all) {
+			memcpy(page_address(bv->bv_page), addr, PAGE_SIZE);
+			addr += PAGE_SIZE;
+		}
 
 		bch_submit_bbio(b->bio, b->c, &k.key, 0);