Update referenced constant names for Directions

The new constants were introduced in [1] 9f7a4442, but the comment used the
wrong prefix - DIR_ instead of RUN_ in the actual names.

[1] Change-Id Iea8bb46c678a18820e237c90f76007a084c83051
    Commit hash 9f7a4442

Test: comment update, no tests performed
Change-Id: I4e13600b16ebd9be7ac40cf6c6292ea13f0806c2