md/raid5: set reshape_position correctly when reshape starts.

As the internal reshape_progress counter is the main driver
for reshape, the fact that reshape_position sometimes starts with the
wrong value has minimal effect. It is visible in sysfs and that
is all.

Signed-off-by: NeilBrown <[e-mail]>

drivers/md/raid5.c

···
 		spin_unlock_irqrestore(&conf->device_lock, flags);
 	}
 	mddev->raid_disks = conf->raid_disks;
-	mddev->reshape_position = 0;
+	mddev->reshape_position = conf->reshape_progress;
 	set_bit(MD_CHANGE_DEVS, &mddev->flags);
 
 	clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);