qemu: virDomainControllerFind may return 0 if controller found

The return value of virDomainControllerFind >=0 means that
the specific controller was found.
But some functions invoke it and treat 0 as not found.
This patch fix these incorrect invocation.
Signed-off-by: NChen Hanxiao <chenhanxiao@cn.fujitsu.com>

src/qemu/qemu_driver.c

@@ -6626,7 +6626,7 @@ qemuDomainAttachDeviceConfig(virQEMUCapsPtr qemuCaps,
     case VIR_DOMAIN_DEVICE_CONTROLLER:
         controller = dev->data.controller;
         if (virDomainControllerFind(vmdef, controller->type,
-                                    controller->idx) > 0) {
+                                    controller->idx) >= 0) {
             virReportError(VIR_ERR_OPERATION_INVALID, "%s",
                            _("Target already exists"));
             return -1;

src/qemu/qemu_hotplug.c

@@ -358,7 +358,7 @@ int qemuDomainAttachPciControllerDevice(virQEMUDriverPtr driver,
     qemuDomainObjPrivatePtr priv = vm->privateData;
     bool releaseaddr = false;
 
-    if (virDomainControllerFind(vm->def, controller->type, controller->idx) > 0) {
+    if (virDomainControllerFind(vm->def, controller->type, controller->idx) >= 0) {
         virReportError(VIR_ERR_OPERATION_FAILED,
                        _("target %s:%d already exists"),
                        type, controller->idx);