softmmu/physmem: Simplify flatview_write and address_space_access_valid

Remove unuseful local 'result' variables.

Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20211215182421.418374-3-philmd@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>