Fix bugs for prometheus chart (#2915)

Signed-off-by: Ziqi Zhao <zhaoziqi@qiniu.com>

stable/prometheus/Chart.yaml

@@ -1,5 +1,5 @@
 name: prometheus
-version: 4.6.13
+version: 4.6.14
 description: Prometheus is a monitoring system and time series database.
 home: https://prometheus.io/
 icon: https://raw.githubusercontent.com/prometheus/prometheus.github.io/master/assets/prometheus_logo-cb55bb5c346.png

stable/prometheus/templates/server-deployment.yaml

@@ -74,7 +74,7 @@ spec:
             - name: config-volume
               mountPath: /etc/config
             - name: storage-volume
-              mountPath: {{ .Values.alertmanager.persistentVolume.mountPath }}
+              mountPath: {{ .Values.server.persistentVolume.mountPath }}
               subPath: "{{ .Values.server.persistentVolume.subPath }}"
           {{- range .Values.server.extraHostPathMounts }}
             - name: {{ .name }}