ART: Fix Android.cpplint.mk to use scan art/ directory

Currently Android.cpplint.mk doesn't set LOCAL_PATH variable but assumes
that it is initialized properly (see comments before initializing
ART_CPPLINT_SRC variable). Change https://r.android.com/1711019  moved
one of the includes in art/Android.mk file up, before include
Android.cpplint.mk which modified this variable, so currently
'm cpplint-art' call only scans source files in tools/veridex folder

Test: m cpplint-art and m cpplint-art-all
Change-Id: Ic948e029a4365fc49b8ffeb1e67b47ac0dbee182
1 file changed