prep: add ppc-parity write method

Add ppc-parity mmio write method to avoid NULL pointer dereference
issue.

Reported-by: Lei Sun <slei.casper@gmail.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Reviewed-by: Li Qiang <liq3ea@gmail.com>
Message-Id: <20200811114133.672647-5-ppandit@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/ppc/prep_systemio.c

@@ -23,6 +23,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/log.h"
 #include "hw/irq.h"
 #include "hw/isa/isa.h"
 #include "hw/qdev-properties.h"
@@ -235,8 +236,15 @@ static uint64_t ppc_parity_error_readl(void *opaque, hwaddr addr,
     return val;
 }
 
+static void ppc_parity_error_writel(void *opaque, hwaddr addr,
+                                    uint64_t data, unsigned size)
+{
+    qemu_log_mask(LOG_GUEST_ERROR, "%s: invalid access\n", __func__);
+}
+
 static const MemoryRegionOps ppc_parity_error_ops = {
     .read = ppc_parity_error_readl,
+    .write = ppc_parity_error_writel,
     .valid = {
         .min_access_size = 4,
         .max_access_size = 4,