Display storage summary with correct used/total size.

Fixes: 30421727

We need to first initialize sTotalInternalStorage in order to compute
used size for both full blown storage fragment and storage tile summary.

Also fixed a bug where sTotalInteralStorage is incorrectly added
multiple times when there are multiple private volumes.

Change-Id: Iabb869c3184ec0c468aeacea34c804b90b4965f1