Fix error checking in cc2538dk-nvm
Fix error checking in cc2538dk-nvm

The second `err` comparison was useless as `err` was not assigned to the second function return value.

Also fixed whitespaces.
bluerover/6lbr,bluerover/6lbr,bluerover/6lbr,bluerover/6lbr,bluerover/6lbr,bluerover/6lbr,bluerover/6lbr