dm: add missing trace_block_split() to __split_and_process_bio()

Provides useful context about bio splits in blktrace.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm.c

@@ -1655,6 +1655,7 @@ static blk_qc_t __split_and_process_bio(struct mapped_device *md,
 				part_stat_unlock();
 
 				bio_chain(b, bio);
+				trace_block_split(md->queue, b, bio->bi_iter.bi_sector);
 				ret = generic_make_request(bio);
 				break;
 			}