buffer: Update cachedBufferHeader during "initialize"

We know what the bufferheader is after we call "initialize" (as we
clear the buffer before updating the known header). Update
cachedBufferHeader after successful initialization.

Signed-off-by: Brandon Kim <brandonkim@google.com>
Change-Id: Ia4c6f5258b5ccd0294bba267717b8e77c0bf5449
diff --git a/test/buffer_test.cpp b/test/buffer_test.cpp
index e3d5621..e8943a9 100644
--- a/test/buffer_test.cpp
+++ b/test/buffer_test.cpp
@@ -78,6 +78,7 @@
             throw;
         },
         std::runtime_error);
+    EXPECT_NE(bufferImpl->getCachedBufferHeader(), testInitializationHeader);
 
     EXPECT_CALL(*dataInterfaceMockPtr, getMemoryRegionSize())
         .WillOnce(Return(testRegionSize));
@@ -97,6 +98,7 @@
             throw;
         },
         std::runtime_error);
+    EXPECT_NE(bufferImpl->getCachedBufferHeader(), testInitializationHeader);
 }
 
 TEST_F(BufferTest, BufferInitializePass)
@@ -117,6 +119,7 @@
     EXPECT_NO_THROW(bufferImpl->initialize(testBmcInterfaceVersion,
                                            testQueueSize, testUeRegionSize,
                                            testMagicNumber));
+    EXPECT_EQ(bufferImpl->getCachedBufferHeader(), testInitializationHeader);
 }
 
 TEST_F(BufferTest, BufferHeaderReadFail)