UPSTREAM: bpf: fix rcu annotations in compute_effective_progs()

The progs local variable in compute_effective_progs() is marked
as __rcu, which is not correct. This is a local pointer, which
is initialized by bpf_prog_array_alloc(), which also now
returns a generic non-rcu pointer.

The real rcu-protected pointer is *array (array is a pointer
to an RCU-protected pointer), so the assignment should be performed
using rcu_assign_pointer().

Fixes: 324bda9e6c5a ("bpf: multi program support for cgroup+bpf")
Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
(cherry picked from commit 3960f4fd6585608e8cc285d9665821985494e147)
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ie1eec4e3148a4c802759a3f0257dfae4a9333520