Refactor: rename namespace witherspoon to phosphor

This repo now becomes phosphor-power, rename namespace witherspoon to
phosphor to make it generic.

Signed-off-by: Lei YU <mine260309@gmail.com>
Change-Id: Icb9f8a7c33065add99f2bf42ed55745a28fa0424
diff --git a/power-supply/average.hpp b/power-supply/average.hpp
index a61a436..5fdf0b8 100644
--- a/power-supply/average.hpp
+++ b/power-supply/average.hpp
@@ -2,7 +2,7 @@
 #include <functional>
 #include <org/open_power/Sensor/Aggregation/History/Average/server.hpp>
 
-namespace witherspoon
+namespace phosphor
 {
 namespace power
 {
@@ -51,4 +51,4 @@
 
 } // namespace history
 } // namespace power
-} // namespace witherspoon
+} // namespace phosphor