nvdimm-btt: use bvec_kmap_local in btt_rw_integrity

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/20220303111905.321089-7-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvdimm/btt.c

@@ -1163,17 +1163,15 @@ static int btt_rw_integrity(struct btt *btt, struct bio_integrity_payload *bip,
 		 */
 
 		cur_len = min(len, bv.bv_len);
-		mem = kmap_atomic(bv.bv_page);
+		mem = bvec_kmap_local(&bv);
 		if (rw)
-			ret = arena_write_bytes(arena, meta_nsoff,
-					mem + bv.bv_offset, cur_len,
+			ret = arena_write_bytes(arena, meta_nsoff, mem, cur_len,
 					NVDIMM_IO_ATOMIC);
 		else
-			ret = arena_read_bytes(arena, meta_nsoff,
-					mem + bv.bv_offset, cur_len,
+			ret = arena_read_bytes(arena, meta_nsoff, mem, cur_len,
 					NVDIMM_IO_ATOMIC);
 
-		kunmap_atomic(mem);
+		kunmap_local(mem);
 		if (ret)
 			return ret;