Fix the fallocate system call on powerpc to match its unistd.h.

This implies none of these system calls are currently working with the
unistd.h sys call values:
	fallocate
	signalfd
	timerfd
	eventfd
	sync_file_range2

Signed-off-by: Patrick Mansfield <patmans@us.ibm.com>
Acked-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>