s390: Fix cpu refactoring fallout.

Commit 259186a7 "cpu: Move halted and interrupt_request fields to CPUState"
seems to have missed one instance in target-s390x/kvm.c:

/home/cohuck/git/qemu/target-s390x/kvm.c: In function ‘kvm_arch_process_async_events’:
/home/cohuck/git/qemu/target-s390x/kvm.c:319: error: ‘CPUS390XState’ has no member named ‘halted’
/home/cohuck/git/qemu/target-s390x/kvm.c:320: warning: control reaches end of non-void function
make[1]: *** [target-s390x/kvm.o] Error 1

Let's just switch to cs->halted.
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Acked-by: NAlexander Graf <agraf@suse.de>
Acked-by: NAndreas Färber <afaerber@suse.de>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

target-s390x/kvm.c

@@ -315,8 +315,7 @@ void kvm_arch_post_run(CPUState *cpu, struct kvm_run *run)
 
 int kvm_arch_process_async_events(CPUState *cs)
 {
-    S390CPU *cpu = S390_CPU(cs);
-    return cpu->env.halted;
+    return cs->halted;
 }
 
 void kvm_s390_interrupt_internal(S390CPU *cpu, int type, uint32_t parm,