numa: Clean up error reporting in parse_numa()

numa: Clean up error reporting in parse_numa()

Calling error_report() in a function that takes an Error ** argument
is suspicious.  parse_numa() does that, and then fails without setting
an error.  Its caller main(), via qemu_opts_foreach(), is fine with
it, but clean it up anyway.

While there, give parse_numa() internal linkage.

Cc: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20181017082702.5581-29-armbru@redhat.com>