init: fix write_file checkreqprot logic error

write_file() returned -errno on error, not -1. Callers who check for
-1 would falsely believe that the write was successful when it wasn't.
Fixup write_file so that it return -1 on error consistent
with other functions.

Change-Id: Ic51aaf8678d8d97b2606bd171f11b3b11f642e39