7128584: Typo in sun.misc.VM's private directMemory field comment

Reviewed-by: forax, chegar
Contributed-by: NKrystal Mok <sajia@taobao.com>

src/share/classes/sun/misc/VM.java

@@ -168,7 +168,7 @@ public class VM {
     //
     // The initial value of this field is arbitrary; during JRE initialization
     // it will be reset to the value specified on the command line, if any,
-    // otherwise to Runtime.getRuntime.maxDirectMemory().
+    // otherwise to Runtime.getRuntime().maxMemory().
     //
     private static long directMemory = 64 * 1024 * 1024;