elf: Update comments for check_relocs in elf_backend_data

Since

commit 5c3261b0e834647cf9eb555320e20871b7854f98
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Mon Oct 16 03:49:54 2017 -0700

    ELF: Call check_relocs after opening all inputs

check_relocs is called after opening all inputs.

	* elf-bfd.h (elf_backend_data::check_relocs): Update comments.
1 file changed