Fix accounting for .vdex in dumpsys meminfo

Before it was showing up in "Other mmap" instead. Now it is correctly
showing up in ".dex mmap".

Bug: 30937355
Test: N6P booting, dumpsys meminfo -d

(cherry picked from commit 946ebbcc)

Change-Id: I49a202deda3fc34a94247825dc059b8a854ba61a