sensors/zones: place in namespace and cleanup

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I527dbc8477a232945f696227a7b0b2adbee45175
diff --git a/pid/builder.cpp b/pid/builder.cpp
index 0ffadf1..b76d134 100644
--- a/pid/builder.cpp
+++ b/pid/builder.cpp
@@ -28,6 +28,9 @@
 #include <memory>
 #include <unordered_map>
 
+namespace pid_control
+{
+
 static constexpr bool deferSignals = true;
 static constexpr auto objectPath = "/xyz/openbmc_project/settings/fanctrl/zone";
 
@@ -135,3 +138,5 @@
 
     return zones;
 }
+
+} // namespace pid_control