syscall: fix build
syscall: fix build

I missed the API change in the last FreeBSD CL, but the tool caught it.

TBR=bradfitz
CC=golang-dev
http://codereview.appspot.com/6331063

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang