dm-crypt: don't clear bvec->bv_page in crypt_free_buffer_pages()

The bio is always freed after running crypt_free_buffer_pages(), so it
isn't necessary to clear bv->bv_page.

Cc: Mike Snitzer <snitzer@redhat.com>
Cc:dm-devel@redhat.com
Signed-off-by: NMing Lei <ming.lei@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/md/dm-crypt.c

@@ -1446,7 +1446,6 @@ static void crypt_free_buffer_pages(struct crypt_config *cc, struct bio *clone)
 	bio_for_each_segment_all(bv, clone, i) {
 		BUG_ON(!bv->bv_page);
 		mempool_free(bv->bv_page, cc->page_pool);
-		bv->bv_page = NULL;
 	}
 }