virtio-pci: drop unused wmb macro

The implementation is wrong for kvm, and it's unused anyway.
Drop it.
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Message-id: 20130528102023.GA30055@redhat.com
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/virtio/virtio-pci.c

@@ -89,12 +89,6 @@
 /* Flags track per-device state like workarounds for quirks in older guests. */
 #define VIRTIO_PCI_FLAG_BUS_MASTER_BUG  (1 << 0)
 
-/* QEMU doesn't strictly need write barriers since everything runs in
- * lock-step.  We'll leave the calls to wmb() in though to make it obvious for
- * KVM or if kqemu gets SMP support.
- */
-#define wmb() do { } while (0)
-
 /* HACK for virtio to determine if it's running a big endian guest */
 bool virtio_is_big_endian(void);