Change strerror(ret) to strerror(-ret).

src/mesa/drivers/dri/intel/intel_batchbuffer.c

@@ -138,7 +138,7 @@ do_flush_locked(struct intel_context *intel)
    }
 
    if (ret != 0) {
-      fprintf(stderr, "intel_do_flush_locked failed: %s\n", strerror(ret));
+      fprintf(stderr, "intel_do_flush_locked failed: %s\n", strerror(-ret));
       exit(1);
    }
    intel->vtbl.new_batch(intel);