RFR: JDK-8066260 - I2CSlave - wrong return value in trasfer method

[alexey mironov]

issue: https://bugs.openjdk.java.net/browse/JDK-8066260 
<https://bugs.openjdk.java.net/browse/JDK-8065776>
webrev: http://cr.openjdk.java.net/~amironov/8066260/ 
<https://bugs.openjdk.java.net/browse/JDK-8065776>

Please review the changes made in order to fix wrong return value in 
I2CSlaveImpl.

Regards,
Alexey