Rename ddir_nr -> ddir_seq_nr

Another mode will be added, so lets rename this one internally
to make the distinction clear.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/io_u.c b/io_u.c
index f27cdda..bb00559 100644
--- a/io_u.c
+++ b/io_u.c
@@ -54,7 +54,7 @@
 		 * If we have a mixed random workload, we may
 		 * encounter blocks we already did IO to.
 		 */
-		if ((td->o.ddir_nr == 1) && !random_map_free(f, block))
+		if ((td->o.ddir_seq_nr == 1) && !random_map_free(f, block))
 			break;
 
 		idx = RAND_MAP_IDX(f, block);
@@ -201,8 +201,8 @@
 	unsigned long long b;
 	enum fio_ddir ddir = io_u->ddir;
 
-	if (td_random(td) && (td->o.ddir_nr && !--td->ddir_nr)) {
-		td->ddir_nr = td->o.ddir_nr;
+	if (td_random(td) && (td->o.ddir_seq_nr && !--td->ddir_seq_nr)) {
+		td->ddir_seq_nr = td->o.ddir_seq_nr;
 
 		if (get_next_rand_offset(td, f, ddir, &b)) {
 			dprint(FD_IO, "%s: getting rand offset failed\n",