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/test/nvtest.cpp b/test/nvtest.cpp
index a7a102b..bd02332 100644
--- a/test/nvtest.cpp
+++ b/test/nvtest.cpp
@@ -19,7 +19,7 @@
 
 TEST(NamesValuesTest, TestValues)
 {
-    witherspoon::power::util::NamesValues nv;
+    phosphor::power::util::NamesValues nv;
 
     std::string expected;
     EXPECT_EQ(nv.get(), expected); // empty