qemu: hotplug: Fix asynchronous unplug of 'shmem'

commit 5c81c342 forgot to skip the detaching of the shmem backend
when async unplug is requested which meant that we've tried to unplug
the backend prior to delivery of the DEVICE_DELETED event.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1618622Signed-off-by: NPeter Krempa <pkrempa@redhat.com>

src/qemu/qemu_hotplug.c

@@ -5479,11 +5479,16 @@ qemuDomainDetachShmemDevice(virQEMUDriverPtr driver,
     if (qemuDomainObjExitMonitor(driver, vm) < 0)
         goto cleanup;
 
-    if ((ret = qemuDomainWaitForDeviceRemoval(vm)) == 1)
-        ret = qemuDomainRemoveShmemDevice(driver, vm, shmem);
+    if (async) {
+        ret = 0;
+    } else {
+        if ((ret = qemuDomainWaitForDeviceRemoval(vm)) == 1)
+            ret = qemuDomainRemoveShmemDevice(driver, vm, shmem);
+    }
 
  cleanup:
-    qemuDomainResetDeviceRemoval(vm);
+    if (!async)
+        qemuDomainResetDeviceRemoval(vm);
     return ret;
 }