resolve_gitlink_packed_ref(): fix mismerge

resolve_gitlink_packed_ref(): fix mismerge

2c5c66b (Merge branch 'jp/get-ref-dir-unsorted', 2011-10-10) merged a
topic that forked from the mainline before a new helper function
get_packed_refs() refactored code to read packed-refs file. The merge made
the call to the helper function with an incorrect argument. The parameter
to the function has to be a path to the submodule.

Fix the mismerge.

Helped-by: Mark Levedahl <mlevedahl@gmail.com>
Helped-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>