vl: Clean up error reporting in parse_add_fd()

vl: Clean up error reporting in parse_add_fd()

Calling error_report() in a function that takes an Error ** argument
is suspicious.  parse_add_fd() 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.

Also change call of cleanup_add_fd(), which can't fail, for symmetry.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20181017082702.5581-19-armbru@redhat.com>