staging: lustre: replace cfs_get_random_bytes calls with get_random_byte()

The cfs_get_random_bytes() interface adds nothing of value
to get_random_byte() (which it uses internally).  So just use the
standard interface.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>