md/raid5: always set conf->prev_chunk_sectors and ->prev_algo

These aren't really needed when no reshape is happening,
but it is safer to have them always set to a meaningful value.
The next patch will use ->prev_chunk_sectors without checking
if a reshape is happening (because that makes the code simpler),
and this patch makes that safe.

Signed-off-by: NeilBrown <neilb@suse.com>
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 256b05d..e543bfd 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -6568,6 +6568,9 @@
 	if (conf->reshape_progress != MaxSector) {
 		conf->prev_chunk_sectors = mddev->chunk_sectors;
 		conf->prev_algo = mddev->layout;
+	} else {
+		conf->prev_chunk_sectors = conf->chunk_sectors;
+		conf->prev_algo = conf->algorithm;
 	}
 
 	conf->min_nr_stripes = NR_STRIPES;