wcn36xx: fix incorrect assignment to msg_body.min_ch_time

wcn36xx: fix incorrect assignment to msg_body.min_ch_time

The second assignment to msg_body.min_ch_time is incorrect, it
should actually be to msg_body.max_ch_time.

Thanks to Bjorn Andersson for identifying the correct way to fix
this as my original fix was incorrect.

Detected by CoverityScan, CID#1463042 ("Unused Value")

Fixes: 2f3bef4b247e ("wcn36xx: Add hardware scan offload support")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>