Fix a bad link target in Diffusion content search results

Summary: See https://discourse.phabricator-community.org/t/broken-links-in-diffusion-pattern-search-results-page/757. This links to the display path, which is incorrect.

Test Plan:

• In any repository, browsed into a directory.
• Used pattern search to search for something that hits results.
• Clicked the title (filename/path) of a result table.
  • Before patch: URL omits path context, 404 or wrong result.
  • After patch: taken to proper page.

Reviewers: amckinley

Reviewed By: amckinley

Differential Revision: https://secure.phabricator.com/D18779