sensors/zones: place in namespace and cleanup

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I527dbc8477a232945f696227a7b0b2adbee45175
diff --git a/pid/zone.hpp b/pid/zone.hpp
index dc2ceb8..9dc433a 100644
--- a/pid/zone.hpp
+++ b/pid/zone.hpp
@@ -23,6 +23,9 @@
 using ModeInterface = sdbusplus::xyz::openbmc_project::Control::server::Mode;
 using ModeObject = ServerObject<ModeInterface>;
 
+namespace pid_control
+{
+
 class ZoneInterface
 {
   public:
@@ -119,3 +122,5 @@
     std::vector<std::unique_ptr<Controller>> _fans;
     std::vector<std::unique_ptr<Controller>> _thermals;
 };
+
+} // namespace pid_control