Improve mixed random append option

If we set ->ddir_nr to o.ddir_nr initally, we can remove the double
else in get_next_offset().

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/init.c b/init.c
index 911ee32..2704032 100644
--- a/init.c
+++ b/init.c
@@ -424,6 +424,7 @@
 	td->ts.clat_stat[0].min_val = td->ts.clat_stat[1].min_val = ULONG_MAX;
 	td->ts.slat_stat[0].min_val = td->ts.slat_stat[1].min_val = ULONG_MAX;
 	td->ts.bw_stat[0].min_val = td->ts.bw_stat[1].min_val = ULONG_MAX;
+	td->ddir_nr = td->o.ddir_nr;
 
 	if ((td->o.stonewall || td->o.numjobs > 1 || td->o.new_group)
 	     && prev_group_jobs) {