fix(findmydevice): Fix wrong namespace in kustomization

This patch fixes a copy & paste mistake

apps/base/findmydevice/kustomization.yaml

 apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
-namespace: mastodon
+namespace: findmydevice
 resources:
   - namespace.yaml
   - release.yaml