PEL: Rename Section::flattenedSize

cppcheck was complaining about how flattenedSize() was in both the base
class Section and all of its derived classes even though it wasn't
virtual.

Change-Id: I5cce8c6534e696f30c2c6141a50665d11a13eff0
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/extensions/openpower-pels/section.hpp b/extensions/openpower-pels/section.hpp
index 4c48bbf..ab0ad59 100644
--- a/extensions/openpower-pels/section.hpp
+++ b/extensions/openpower-pels/section.hpp
@@ -125,7 +125,7 @@
     /**
      * @brief Returns the flattened size of the section header
      */
-    static constexpr size_t flattenedSize()
+    static constexpr size_t headerSize()
     {
         return SectionHeader::flattenedSize();
     }