ISPN-2658 Fix expected value MarshalledValueTest.testModificationsOnSame...

...CustomKey

After fixing ISPN-2803 the key is not added in StateConsumerImpl.updatedKeys so no extra comparison (and serialization) is done. Decrease expected value by 1.

Please integrate in master and 5.2.x (anistor/t_2658_52).

JIRA: https://issues.jboss.org/browse/ISPN-2658