md/raid5: make sure curr_sync_completes is uptodate when reshape starts

This value is visible through sysfs and is used by mdadm
when it manages a reshape (backing up data that is about to be
rearranged). So it is important that it is always correct.
Current it does not get updated properly when a reshape
starts which can cause problems when assembling an array
that is in the middle of being reshaped.

This is suitable for 2.6.31.y stable kernels.

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

drivers/md/raid5.c

···
 			sector_nr = conf->reshape_progress;
 		sector_div(sector_nr, new_data_disks);
 		if (sector_nr) {
+			mddev->curr_resync_completed = sector_nr;
+			sysfs_notify(&mddev->kobj, NULL, "sync_completed");
 			*skipped = 1;
 			return sector_nr;
 		}