fix(ota): Correctly select the partition to write to

There was an off-by-one error selecting the new partition, meaning the OTA
update would write to the second partition but the boot would be set to the same
one we're currently in.

I believe this should fix jpirnay/crosspoint-reader#112

src/activities/settings/OtaUpdateActivity.cpp

@@ -164,6 +164,10 @@ void OtaUpdateActivity::render(RenderLock&&) {
   }
 
   renderer.displayBuffer();
+
+  if (state == FINISHED) {
+    state = SHUTTING_DOWN;
+  }
 }
 
 void OtaUpdateActivity::loop() {