storage: Improve code consistency between backends

This improves the code consistency around freeing vol->target.path in
createVol implementations.

src/storage/storage_backend_logical.c

@@ -921,9 +921,7 @@ virStorageBackendLogicalCreateVol(virConnectPtr conn,
 
     vol->type = VIR_STORAGE_VOL_BLOCK;
 
-    /* A target path passed to CreateVol has no meaning */
     VIR_FREE(vol->target.path);
-
     if (virAsprintf(&vol->target.path, "%s/%s",
                     pool->def->target.path,
                     vol->name) == -1)

src/storage/storage_backend_zfs.c

@@ -303,11 +303,7 @@ virStorageBackendZFSCreateVol(virConnectPtr conn ATTRIBUTE_UNUSED,
 
     vol->type = VIR_STORAGE_VOL_BLOCK;
 
-    if (vol->target.path != NULL) {
-        /* A target path passed to CreateVol has no meaning */
-        VIR_FREE(vol->target.path);
-    }
-
+    VIR_FREE(vol->target.path);
     if (virAsprintf(&vol->target.path, "%s/%s",
                     pool->def->target.path, vol->name) == -1)
         return -1;