md: add MODULE_DESCRIPTION for all md related modules.

Suggested by  Oren Held <orenhe@il.ibm.com>

Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 5c71a46..d119b7b 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2408,6 +2408,7 @@
 module_init(raid_init);
 module_exit(raid_exit);
 MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("RAID10 (striped mirror) personality for MD");
 MODULE_ALIAS("md-personality-9"); /* RAID10 */
 MODULE_ALIAS("md-raid10");
 MODULE_ALIAS("md-level-10");