hostdev: add virObject field to virHostdevManager struct

Commit 6b306d66 converted virHostdevManager to a virObject, but
missed adding a virObject field to the virHostdevManager struct.
Result is memory corruption when taking a reference on an instance
of the object, where atomic inc is done on the stateDir field.
Later use of stateDir crashes libvirtd.

src/util/virhostdev.h

@@ -45,6 +45,8 @@ typedef enum {
 typedef struct _virHostdevManager virHostdevManager;
 typedef virHostdevManager *virHostdevManagerPtr;
 struct _virHostdevManager {
+    virObject parent;
+
     char *stateDir;
 
     virPCIDeviceListPtr activePCIHostdevs;