Grow: don't print message if unfreezing fails.

This is most likely to happen if the array has been stopped,
in which case the error is pointless.

Reported-by: Patrik Horník <patrik@dsl.sk>
Signed-off-by: NeilBrown <neilb@suse.de>

Grow.c

@@ -623,8 +623,6 @@ static void unfreeze(struct supertype *st)
 
 		if (sra)
 			sysfs_set_str(sra, NULL, "sync_action", "idle");
-		else
-			fprintf(stderr, Name ": failed to unfreeze array\n");
 		sysfs_free(sra);
 	}
 }