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/utility.hpp b/utility.hpp
index df66852..78b9425 100644
--- a/utility.hpp
+++ b/utility.hpp
@@ -6,7 +6,7 @@
 #include <sdbusplus/bus.hpp>
 #include <string>
 
-namespace witherspoon
+namespace phosphor
 {
 namespace power
 {
@@ -116,4 +116,4 @@
 
 } // namespace util
 } // namespace power
-} // namespace witherspoon
+} // namespace phosphor