sysfs: fixed sysfs_freeze_array array to work properly with Manage_subdevs.

sysfs: fixed sysfs_freeze_array array to work properly with Manage_subdevs.

If the array is already frozen when Manage_subdevs is called we don't
want it to unfreeze the array.
This is because Grow calls Manage_subdevs to add devices to an array
being reshaped, and the array must stay frozen over this call.

So if sysfs_freeze_array find the array to be frozen it returns '0',
meaning that it didn't and cannot freeze it.  Then the caller will not
try to unfreeze, which is good.

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