storage: Fix coverity warning

After commit e808d3f227 cbdata is always available here, so the
check is pointless

src/storage/storage_driver.c

@@ -2442,12 +2442,10 @@ storageVolUpload(virStorageVolPtr obj,
     /* Add cleanup callback - call after uploadVol since the stream
      * is then fully set up
      */
-    if (cbdata) {
     virFDStreamSetInternalCloseCb(stream,
                                   virStorageVolFDStreamCloseCb,
                                   cbdata, NULL);
     cbdata = NULL;
-    }
 
  cleanup:
     virStoragePoolObjUnlock(pool);