md: centralize ->array_sectors modifications

Get personalities out of the business of directly modifying
->array_sectors.  Lays groundwork to introduce policy on when
->array_sectors can be modified.

Reviewed-by: Andre Noll <maan@systemlinux.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
index bb0df6a..6f7e538 100644
--- a/drivers/md/raid0.c
+++ b/drivers/md/raid0.c
@@ -306,7 +306,7 @@
 		goto out_free_conf;
 
 	/* calculate array device size */
-	mddev->array_sectors = raid0_size(mddev, 0, 0);
+	md_set_array_sectors(mddev, raid0_size(mddev, 0, 0));
 
 	printk(KERN_INFO "raid0 : md_size is %llu sectors.\n",
 		(unsigned long long)mddev->array_sectors);