Fix bug that would prevent us from reserving right amount of space.

Bug: 132403230
Test: inspect dmesg output:
[   10.762678] init: [libfs_mgr]Setting reserved block count on
/dev/block/dm-2 to 32768
[   10.782652] tune2fs: Setting reserved blocks gid to 1065\x0a
[   10.782655] tune2fs: Setting reserved blocks count to 32768\x0a

Change-Id: Id366d478bdd8a748bb1ba97d08a3b52e3cdd1efb