ipw2x00: make ipw_qos_association_resp() void

Fix the following coccicheck warning:

drivers/net/wireless/intel/ipw2x00/ipw2200.c:7048:5-8: Unneeded
variable: "ret". Return "0" on line 7055

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200410090850.27025-1-yanaijie@huawei.com