Fix a typo when reporting size change wrt a decl-only class

Fix a typo when reporting size change wrt a decl-only class

When a class is compared to its decl-only counterpart, if the user
doesn't want to see decl-only class related change, then do not report
any size change that might result from it.

This was already meant to be implemented but there was a typo.  Fixed
thus.

	* src/abg-comparison.cc (report_size_and_alignment_changes): Fix
	typo.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>