LU-9859 libcfs: replace cfs_get_random_bytes calls with get_random_byte()

LU-9859 libcfs: 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.

Linux-commit: e904f839cdb04d1b314753a83a6e58146e315c66

Change-Id: I48e153d7658f0f616afe4e884faeb09c2dbdcd03
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-on: https://review.whamcloud.com/35234
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Petros Koutoupis <pkoutoupis@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>