[yaml2obj][tests] Fix overly restrictive od output check

Summary:
rL364517 introduced further instances of `od` output checking of the
kind previously corrected by rL363829. This patch corrects the issue by
suppressing output of the input offset. The check remains sufficiently
sensitive to test for the intended value of the specific byte since the
relevant byte value is the only output we are expecting from `od`.

Reviewers: grimar, xingxue, daltenty, jasonliu, jhenderson, MaskRay

Reviewed By: grimar, MaskRay

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65680

llvm-svn: 367862