8264502: (fc) FileDispatcherImpl.setDirect0 might return uninitialized variable on some platforms

Reviewed-by: alanb, bpb, michaelm

src/java.base/unix/native/libnio/ch/FileDispatcherImpl.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2021, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -375,7 +375,7 @@ Java_sun_nio_ch_FileDispatcherImpl_setDirect0(JNIEnv *env, jclass clazz,
         result = (int)file_stat.f_frsize;
     }
 #else
-    result == -1;
+    result = -1;
 #endif
     return result;
 }