Add a default target for the example
Add a default target for the example

This file set the default target to be the cc2538dk for the i2c-example.

bluerover/6lbr,bluerover/6lbr,bluerover/6lbr,bluerover/6lbr,bluerover/6lbr,bluerover/6lbr,bluerover/6lbr