Replace $(call my-dir) with a string literal

This is so that we can set LOCAL_PATH to the result
of my-dir, as LOCAL_PATH can only be set to a string
literal of the exact value of LOCAL_PATH.

It's probably also the correct choice to start phasing
out LOCAL_PATH.

Bug: 214405650
Test: go test
Change-Id: Ia97d7fedf4ce62643921d90a176e65edd4e2fce6