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/extended_user_data.hpp b/extensions/openpower-pels/extended_user_data.hpp
index 8822e7b..b2803e2 100644
--- a/extensions/openpower-pels/extended_user_data.hpp
+++ b/extensions/openpower-pels/extended_user_data.hpp
@@ -68,7 +68,7 @@
      */
     size_t flattenedSize()
     {
-        return Section::flattenedSize() + sizeof(_creatorID) +
+        return Section::headerSize() + sizeof(_creatorID) +
                sizeof(_reserved1B) + sizeof(_reserved2B) + _data.size();
     }
 
@@ -124,7 +124,7 @@
             {
                 // Use shrink to handle 4B alignment and update the header size
                 auto status =
-                    shrink(Section::flattenedSize() + 4 + newData.size());
+                    shrink(Section::headerSize() + 4 + newData.size());
                 if (status)
                 {
                     origDataSize = _data.size();