Explicitly name DT_RPATH.

The specific case of finding a DT_RPATH entry is a pretty common harmless
warning. An alternative to this change would be to just add a case to the
switch for DT_RPATH to just silently ignore it, since it's never been
supported and is deprecated anyway.

Bug: N/A
Test: builds
Change-Id: I01986da8f1f8d411fc2ea32d492c53b9f4488c72