qemu: Fix double free when live-attaching shmem

Function qemuDomainAttachShmemDevice() steals the device data if the
hotplug was successful, but the condition checked for unsuccessful
execution otherwise.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>

src/qemu/qemu_driver.c

@@ -7615,7 +7615,7 @@ qemuDomainAttachDeviceLive(virDomainObjPtr vm,
     case VIR_DOMAIN_DEVICE_SHMEM:
         ret = qemuDomainAttachShmemDevice(driver, vm,
                                           dev->data.shmem);
-        if (ret < 0) {
+        if (!ret) {
             alias = dev->data.shmem->info.alias;
             dev->data.shmem = NULL;
         }