hw/ppc/spapr_rtas: Access MachineState via SpaprMachineState argument

We received a SpaprMachineState argument. Since SpaprMachineState
inherits of MachineState, use it instead of calling qdev_get_machine.
Reviewed-by: NGreg Kurz <groug@kaod.org>
Acked-by: NDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200121110349.25842-3-philmd@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/ppc/spapr_rtas.c

@@ -267,7 +267,7 @@ static void rtas_ibm_get_system_parameter(PowerPCCPU *cpu,
                                           uint32_t nret, target_ulong rets)
 {
     PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
-    MachineState *ms = MACHINE(qdev_get_machine());
+    MachineState *ms = MACHINE(spapr);
     unsigned int max_cpus = ms->smp.max_cpus;
     target_ulong parameter = rtas_ld(args, 0);
     target_ulong buffer = rtas_ld(args, 1);