megasas: Add write function to handle write access to PCI BAR 3

This patch fixes a QEMU SEGFAULT when a write operation is performed on
the memory region of the PCI BAR 3 (base address space).
When a writeb(0xe0000000) is performed the .write function is invoked to
handle the write access, however, since the .write is not initialised,
the call to 0, causes QEMU to SEGFAULT.

Signed-off-by: Salva Peiró <speirofr@gmail.com>
Acked-by: Hannes Reinecke <hare@suse.com>
Message-Id: <1437987112-24744-1-git-send-email-speirofr@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/scsi/megasas.c

@@ -2202,8 +2202,15 @@ static uint64_t megasas_queue_read(void *opaque, hwaddr addr,
     return 0;
 }
 
+static void megasas_queue_write(void *opaque, hwaddr addr,
+                               uint64_t val, unsigned size)
+{
+    return;
+}
+
 static const MemoryRegionOps megasas_queue_ops = {
     .read = megasas_queue_read,
+    .write = megasas_queue_write,
     .endianness = DEVICE_LITTLE_ENDIAN,
     .impl = {
         .min_access_size = 8,