xcalloc() takes two arguments: the number of elements and their size.
http-push passes the arguments in reverse order, passing the size
of a repo, followed by the number to allocate.

Rearrange them so they are in the correct order.
Signed-off-by: NBrian Gesiak <modocache@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>