sun4u: add power_mem_read routine

Define skeleton 'power_mem_read' routine. Avoid NULL dereference.

Reported-by: Fakhri Zulkifli <mohdfakhrizulkifli@gmail.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
(cherry picked from commit ad280559c6)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

hw/sparc64/sun4u.c

@@ -214,6 +214,11 @@ typedef struct PowerDevice {
 } PowerDevice;
 
 /* Power */
+static uint64_t power_mem_read(void *opaque, hwaddr addr, unsigned size)
+{
+    return 0;
+}
+
 static void power_mem_write(void *opaque, hwaddr addr,
                             uint64_t val, unsigned size)
 {
@@ -224,6 +229,7 @@ static void power_mem_write(void *opaque, hwaddr addr,
 }
 
 static const MemoryRegionOps power_mem_ops = {
+    .read = power_mem_read,
     .write = power_mem_write,
     .endianness = DEVICE_NATIVE_ENDIAN,
     .valid = {