lowmemorykiller: make perms 0220

Set

* /sys/module/lowmemorykiller/parameters/adj
* /sys/module/lowmemorykiller/parameters/minfree

to 0220. This better indicates that these files are only intended
to be written to, never read.

Change-Id: I9ef054f032b3955e04128fc1a472a17c7b1fa792