[llvm-readobj] - Fix a TODO in elf-reloc-zero-name-or-value.test.

The "TODO" mentioned was:

"Add test for symbol with no name but with a value once yaml2obj allows
referencing symbols with no name from relocations."

We can do it now.

Differential revision: https://reviews.llvm.org/D67609

llvm-svn: 372087