zd1201: simplify the return expression of zd1201_set_maxassoc()

Simplify the return expression.

Signed-off-by: Qinglang Miao <miaoqinglang@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200921131115.93504-1-miaoqinglang@huawei.com