Grow: fix hang when growing a RAID5.

Since:

commit 84d11e6c6a
Author: NeilBrown <neilb@suse.de>
Date:   Thu Aug 1 11:16:14 2013 +1000

    Grow: exit background thread cleanly on SIGTERM.

removed the setting of "sync_max" from abort_reshape() we need
to do it explicitly here.

Signed-off-by: NeilBrown <neilb@suse.de>

Grow.c

@@ -4262,6 +4262,7 @@ int child_monitor(int afd, struct mdinfo *sra, struct reshape *reshape,
 		}
 		if (rv == 0 && increasing && !st->ss->external) {
 			/* No longer need to monitor this reshape */
+			sysfs_set_str(sra, NULL, "sync_max", "max");
 			done = 1;
 			break;
 		}