ads2gas_apple.pl: Reduce differences to ads2gas.pl

Avoid substitution of substrings by using \b to make sure the
substituted strings are at word boundaries.

This is an adaption of the corresponding changes to ads2gas.pl
from 7ebcaeb0fa.

Change-Id: I52160e8ba0373d4779d5fc3b0c384ca5c51c7b13