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/pmbus.cpp b/pmbus.cpp
index f755e99..b0de16d 100644
--- a/pmbus.cpp
+++ b/pmbus.cpp
@@ -22,7 +22,7 @@
 #include <xyz/openbmc_project/Common/Device/error.hpp>
 #include <xyz/openbmc_project/Common/error.hpp>
 
-namespace witherspoon
+namespace phosphor
 {
 namespace pmbus
 {
@@ -336,4 +336,4 @@
 }
 
 } // namespace pmbus
-} // namespace witherspoon
+} // namespace phosphor