dm: rename map_info flush_request to target_request_nr

'target_request_nr' is a more generic name that reflects the fact that
it will be used for both flush and discard support.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 96feada..5974d30 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1692,7 +1692,7 @@
 	chunk_t chunk;
 
 	if (unlikely(bio_empty_barrier(bio))) {
-		if (!map_context->flush_request)
+		if (!map_context->target_request_nr)
 			bio->bi_bdev = s->origin->bdev;
 		else
 			bio->bi_bdev = s->cow->bdev;