pvpanic: use FWCfgState explicitly

Use the type-safe FWCfgState structure instead
of the unsafe void *.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/misc/pvpanic.c

@@ -90,7 +90,7 @@ static int pvpanic_isa_initfn(ISADevice *dev)
 {
     PVPanicState *s = ISA_PVPANIC_DEVICE(dev);
     static bool port_configured;
-    void *fw_cfg;
+    FWCfgState *fw_cfg;
 
     memory_region_init_io(&s->io, &pvpanic_ops, s, "pvpanic", 1);
     isa_register_ioport(dev, &s->io, s->ioport);