Fix return value of virCgroupGetPercpuStats

We need to return the number of successfully populated stats,
not the nparams supplied by the user.

src/util/vircgroup.c

@@ -2897,7 +2897,7 @@ virCgroupGetPercpuStats(virCgroupPtr group,
             goto cleanup;
     }
 
-    rv = nparams;
+    rv = param_idx + 1;
 
  cleanup:
     VIR_FREE(buf);