blame.c: replace instance of !oidcmp for oideq

0906ac2b (blame: use changed-path Bloom filters, 2020-04-16)
introduced a call to oidcmp() that should have been oideq(), which
was introduced in 14438c44 (introduce hasheq() and oideq(),
2018-08-28).

Signed-off-by: Edmundo Carmona Antoranz <eantoranz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>