[Plot] Fix wiring on plot updater

Fix usages of the plot updater, introduced to track real-time
telemetry to remove the need to cache values elsewhere. This
allows memory usage to be decreased for WTD-751.

platform/features/plot/res/templates/plot.html

@@ -113,7 +113,7 @@
 
                 </div>
 
-                <span class="t-wait-spinner loading" ng-show="plot.isRequestPending">
+                <span class="t-wait-spinner loading" ng-show="plot.isRequestPending()">
                 </span>
             </div>
             <div ng-if="$last" class="gl-plot-axis-area gl-plot-x">