[incfs] Use the new IncFs_MakeDirs() function

This gets rid of annoying warnings in logcat about not being
able to create a directory and then directory already existing

Bug: 153704006
Test: atest IncrementalServiceTest
Test: adb install megacity.apk
Change-Id: Ib718960287f93cb383c06c9b9e3d0abf1ec42916