Category breakdown size should match total size.

The system apps' base size was not being properly attributed
to the system. This was causing the storage to go totally
unattributed (and causing roughly a 1GB gap in sizes.) On my
test device, the sizes now sum properly.

Change-Id: Ibc13015e40f854090a7a3ec09eef4c5c52918e0f
Fixes: 35144717
Test: Settings robo