gdb/elfread.c: Use bfd filename instead of objfile->original_name

gdb/elfread.c: Use bfd filename instead of objfile->original_name

The call to debuginfod_debuginfo_query in elf_symfile_read is given
objfile->original_name as the filename to print when downloading the
objfile's debuginfo.

In some cases original_name is prefixed with gdb's working directory
even though the objfile is not located in the working directory. This
causes debuginfod to display the wrong path of the objfile during a download.

Fix this by using the objfile's bfd filename instead.