java: Fix superclass init
java: Fix superclass init

Make sure ->super is initialized to nullptr if a class does not have a
superclass.

Spotted by Valgrind.

Signed-off-by: Pekka Enberg <add4fcd06328a394f0ad91feda7ee057316dc5ed@kernel.org>

penberg/hornet,penberg/hornet,penberg/hornet,penberg/hornet