[s390x] Test bit "in-memory" in case of DiagnoseSyncOnValueBasedClasses

in macroAssembler_s390.cpp:

  if (DiagnoseSyncOnValueBasedClasses != 0) {
    load_klass(Z_R1_scratch, oop);
    z_l(Z_R1_scratch, Address(Z_R1_scratch, Klass::access_flags_offset()));
    assert((JVM_ACC_IS_VALUE_BASED_CLASS & 0xFFFF) == 0, "or change following instruction");
    z_nilh(Z_R1_scratch, JVM_ACC_IS_VALUE_BASED_CLASS >> 16);
    z_brne(done);
  }

here load instruction could be removed if we test the bit in the memory itself.