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 <[e-mail]>
Reviewed-by: Ira Weiny <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

drivers/nvdimm/btt.c

···
 		 */
 
 		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;