bpf: Fix bpf_cgroup_from_id() doxygen header

In commit 332ea1f697be ("bpf: Add bpf_cgroup_from_id() kfunc"), a new
bpf_cgroup_from_id() kfunc was added which allows a BPF program to
lookup and acquire a reference to a cgroup from a cgroup id. The
commit's doxygen comment seems to have copy-pasted fields, which causes
BPF kfunc helper documentation to fail to render:

<snip>/helpers.c:2114: warning: Excess function parameter 'cgrp'...
<snip>/helpers.c:2114: warning: Excess function parameter 'level'...

<snip>

<snip>/helpers.c:2114: warning: Excess function parameter 'level'...

This patch fixes the doxygen header.

Fixes: 332ea1f697be ("bpf: Add bpf_cgroup_from_id() kfunc")
Signed-off-by: David Vernet <void@manifault.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20230228152845.294695-1-void@manifault.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>