Fix error case in coffread.c

coffread.c is the last spot (that I know of) that incorrectly calls
perror_with_name when a BFD function fails.  The issue here is that
perror_with_name examines errno, but BFD failures do not set this.
This patch changes this to use error and bfd_errmsg.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31041
Approved-By: Simon Marchi <simon.marchi@efficios.com>