a sealed super class should be more specific

This is a fix to provide proper error even if the binding comes as
BinaryTypeBinding

Change-Id: I51b3e93eca27da67d5b45ad0ebec7950b3f9a93f
Signed-off-by: Kalyan Prasad Tatavarthi <kalyan_prasad@in.ibm.com>
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.core/+/182833
Tested-by: JDT Bot <jdt-bot@eclipse.org>
Reviewed-by: Manoj Palat <manpalat@in.ibm.com>