wl12xx: remove redundant null check on wl->scan.ssid

ssid is an array of u8, so it can never be null, so the null check on
wl->scan.ssid is redundant and can be removed.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>