LU-12671 mdd: rename mdd/sync_perm to sync_permissions

LU-12671 mdd: rename mdd/sync_perm to sync_permissions

Commit e783bbff accidentally renamed a sysfs variable when moving.
Change the sysfs file to it proper name

Test-Parameters: trivial testlist=replay-vbr

Change-Id: I56e0534506271cf6760f775a9c8fa99b12683861
Fixes: e783bbff ("LU-8066 mdd: migrate from proc to sysfs")
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/35851
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Arshad Hussain <arshad.super@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>