msmnile: Allow init write to discard_max_bytes

system/core/rootdir/init.rc
1110:    write /dev/sys/block/by-name/userdata/queue/discard_max_bytes 134217728
1111:    write /dev/sys/block/by-name/rootdisk/queue/discard_max_bytes 134217728

Fixes: avc: denied { write } for comm="init" name="discard_max_bytes"
    dev="sysfs" ino=68814 scontext=u:r:init:s0
    tcontext=u:object_r:sysfs:s0 tclass=file permissive=0
Change-Id: I9cab3cff6db9e660b2805c0da956d005164327d6