Fix typo in pkg_hash_fetch_best_installation_candidate.

A (presumed) typo in pkg_hash_fetch_best_installation_candidate caused the
matching_pkgs vec to be sorted twice, instead of sorting matching_apkgs.
This fixes both the call and the API to match what appears to be intended.

Signed-off-by: Michael Hansen <michael.j.hansen@hp.com>
Signed-off-by: Alejandro del Castillo <alejandro.delcastillo@ni.com>