qemu: Report more accurate error on failure to attach device.

When attaching device from a xml file and the device is mis-configured,
virsh gives mis-leading message "out of memory". This patch fixes this.
Signed-off-by: NEric Blake <eblake@redhat.com>

src/qemu/qemu_command.c

@@ -1496,6 +1496,9 @@ qemuBuildControllerDevStr(virDomainControllerDefPtr def)
     /* We always get an IDE controller, whether we want it or not. */
     case VIR_DOMAIN_CONTROLLER_TYPE_IDE:
     default:
+        qemuReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                        _("Unknown controller type: %s"),
+                        virDomainControllerTypeToString(def->type));
         goto error;
     }
 

src/qemu/qemu_hotplug.c

@@ -260,7 +260,6 @@ int qemuDomainAttachPciControllerDevice(struct qemud_driver *driver,
             goto cleanup;
 
         if (!(devstr = qemuBuildControllerDevStr(controller))) {
-            virReportOOMError();
             goto cleanup;
         }
     }