runtime: change nproc local variable to uint32
runtime: change nproc local variable to uint32

The nproc and ndone fields are uint32.  This makes the type
consistent.

LGTM=minux.ma
R=golang-codereviews, minux.ma
CC=golang-codereviews
https://codereview.appspot.com/79340044

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