pid: stepwisecontroller: add missing override

[pid/controller.hpp:24] -> [pid/stepwisecontroller.hpp:35]: (style) The
function 'getID' overrides a function in a base class but is not marked
with a 'override' specifier.

Change-Id: I27f0853e24f6b25aa50f701ce5fad1ea989b618c
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/pid/stepwisecontroller.hpp b/pid/stepwisecontroller.hpp
index f369397..37606c3 100644
--- a/pid/stepwisecontroller.hpp
+++ b/pid/stepwisecontroller.hpp
@@ -32,7 +32,7 @@
 
     void process(void) override;
 
-    std::string getID(void)
+    std::string getID(void) override
     {
         return _id;
     }