UPSTREAM: bpf: cgroup: fix documentation of __cgroup_bpf_update()

There's a 'not' missing in one paragraph. Add it.

Fixes: 3007098494be ("cgroup: add support for eBPF programs")
Signed-off-by: Daniel Mack <daniel@zonque.org>
Reported-by: Rami Rosen <roszenrami@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Fixes: Change-Id: I3df35d8d3b1261503f9b5bcd90b18c9358f1ac28
       ("cgroup: add support for eBPF programs")
(cherry picked from commit 01ae87eab53675cbdabd5c4d727c4a35e397cce0)
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>