MD: fix invalid stored role for a disk

If we change the number of array's device after device is removed from array,
then add the device back to array, we can see that device is added as active
role instead of spare which we expected.

Please see the below link for details:
https://marc.info/?l=linux-raid&m=153736982015076&w=2

This is caused by that we prefer to use device's previous role which is
recorded by saved_raid_disk, but we should respect the new number of
conf->raid_disks since it could be changed after device is removed.

Reported-by: Gioh Kim <[email protected]>
Tested-by: Gioh Kim <[email protected]>
Acked-by: Guoqing Jiang <[email protected]>
Signed-off-by: Shaohua Li <[email protected]>

Author: shligit

drivers/md/md.c

@@ -1774,6 +1774,10 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
 			} else
 				set_bit(In_sync, &rdev->flags);
 			rdev->raid_disk = role;
+			if (role >= mddev->raid_disks) {
+				rdev->saved_raid_disk = -1;
+				rdev->raid_disk = -1;
+			}
 			break;
 		}
 		if (sb->devflags & WriteMostly1)