vl.c: Remove unnecessary zero-initialization of NUMA globals

There's no need to zero-initialize globals, they are automatically
initialized to zero.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
