bpf: update outdated comment for refactored btf_check_kfunc_arg_match()

bpf: update outdated comment for refactored btf_check_kfunc_arg_match()

The function btf_check_kfunc_arg_match() was refactored into
check_kfunc_args() by commit 00b85860feb8 ("bpf: Rewrite kfunc
argument handling").  Update the comment accordingly.

Assisted-by: unnamed:deepseek-v3.2 coccinelle
Signed-off-by: Kexin Sun <kexinsun@smail.nju.edu.cn>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://lore.kernel.org/r/20260321105658.6006-1-kexinsun@smail.nju.edu.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>