git rev-list: fix invalid typecast

git rev-list: fix invalid typecast

git rev-list passes rev_list_info, not rev_list objects. Without this
fix, rev-list enables or disables the --verify-objects option depending
on a read from an undefined memory location.

Signed-off-by: Clemens Buchacher <drizzd@aon.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>