Fix incorrect memory pool deallocation while using vg_read for files.

We create a separate pool "lvm2 vg_read" for vg_read and we don't use
cmd->mem anymore.

WHATS_NEW

@@ -1,5 +1,6 @@
 Version 2.02.67 -
 ===============================
+  Fix incorrect memory pool deallocation while using vg_read for files.
   Add --type parameter description to the lvcreate man page.
   Replace strncmp kernel version number checks with proper ones.
   Avoid selecting names under /dev/block if there is an alternative.

lib/format_text/format-text.c

@@ -814,7 +814,7 @@ static struct volume_group *_vg_read_file_name(struct format_instance *fid,
 	 * check that it contains the correct volume group.
 	 */
 	if (vgname && strcmp(vgname, vg->name)) {
-		dm_pool_free(fid->fmt->cmd->mem, vg);
+		dm_pool_destroy(vg->vgmem);
 		log_error("'%s' does not contain volume group '%s'.",
 			  read_path, vgname);
 		return NULL;