pack-write: pass repository to `index_pack_lockfile()`

pack-write: pass repository to `index_pack_lockfile()`

The `index_pack_lockfile()` function uses the global `the_repository`
variable to access the repository. To avoid global variable usage, pass
the repository from the layers above.

Altough the layers above could have access to the repository internally,
simply pass in `the_repository`. This avoids any compatibility issues
and bubbles up global variable usage to upper layers which can be
eventually resolved.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>