riscv: fix elf parsing

[Florian Weimer]

* DJ Delorie:

> I think this one is obvious...  it was causing ldconfig to cache all
> libraries with the wrong flags (soft float vs double), thus making the
> cache useless.
>
> 	* sysdeps/unix/sysv/linux/riscv/readelflib.c
>         (process_elf_file): Fix Elf64 flag parsing.

Since the port was released with 2.27, this needs a bug in Bugzilla
(and an eventual backport).  Thanks.