sensors/zones: place in namespace and cleanup

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I527dbc8477a232945f696227a7b0b2adbee45175
diff --git a/pid/ec/pid.cpp b/pid/ec/pid.cpp
index 7d8b403..98968f7 100644
--- a/pid/ec/pid.cpp
+++ b/pid/ec/pid.cpp
@@ -16,6 +16,8 @@
 
 #include "pid.hpp"
 
+namespace pid_control
+{
 namespace ec
 {
 
@@ -119,3 +121,4 @@
 }
 
 } // namespace ec
+} // namespace pid_control