llvm-objdump: Make some error messages more consistent

Most of the version of report_error were quoting the filename and
printing a colon between the file name and the error message, but this
one wasn't doing either of those. Fix the output to be more
consistent.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@285252 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed