ath6kl: fix atomicity in ath6kl_cfg80211_scan_node()

ath6kl_cfg80211_scan_node() was calling cfg80211_inform_bss_frame()
with CFP_KERNEL but the function is executed with a spin lock taken.
This is wrong and the function must use GFP_ATOMIC instead.

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>