RFR: JDK-8048244 - Make DIO buildable with JDK 7

[Jen Dority]

issue: https://bugs.openjdk.java.net/browse/JDK-8048244
webrev: http://cr.openjdk.java.net/~jld/8048244/

Hi All,

Another tiny review needed. Fixed a compilation error that kept device 
io from building with Java 7.

Thanks,
Jen