drbd: use bvec_kmap_local in drbd_csum_bio

Using local kmaps slightly reduces the chances to stray writes, and
the bvec interface cleans up the code a little bit.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/20220303111905.321089-9-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/drbd/drbd_worker.c

@@ -326,9 +326,9 @@ void drbd_csum_bio(struct crypto_shash *tfm, struct bio *bio, void *digest)
 	bio_for_each_segment(bvec, bio, iter) {
 		u8 *src;
 
-		src = kmap_atomic(bvec.bv_page);
-		crypto_shash_update(desc, src + bvec.bv_offset, bvec.bv_len);
-		kunmap_atomic(src);
+		src = bvec_kmap_local(&bvec);
+		crypto_shash_update(desc, src, bvec.bv_len);
+		kunmap_local(src);
 
 		/* REQ_OP_WRITE_SAME has only one segment,
 		 * checksum the payload only once. */