added ERROR code for superblock mismatch

Signed-off-by: Piotr Debski <piotr.debski@intel.com>

src/mngt/ocf_mngt_cache.c

@@ -2277,7 +2277,7 @@ static void _ocf_mngt_activate_compare_superblock_end(
 
 	if (diff) {
 		ocf_cache_log(cache, log_err, "Superblock mismatch!\n");
-		OCF_PL_FINISH_RET(context->pipeline, -OCF_ERR_INVAL);
+		OCF_PL_FINISH_RET(context->pipeline, -OCF_ERR_SUPERBLOCK_MISMATCH);
 	}
 
 	ocf_pipeline_next(context->pipeline);