change /fstab.* perms to 0640

It's safe to change the permissions on files in the root partitions;
incremental OTA now knows how to handle this case.

This reverts commit 08c370cc50e4bdae5a59f4ddfd1e3874bb36579d.

Change-Id: I503bf8ebd037fa9715494c6539e5430eee47acfe
1 file changed