staging: wlan-ng: cfg80211: Move large struct onto the heap

Fixes the following W=1 kernel build warning(s):

 drivers/staging/wlan-ng/cfg80211.c: In function ‘prism2_scan’:
 drivers/staging/wlan-ng/cfg80211.c:388:1: warning: the frame size of 1296 bytes is larger than 1024 bytes [-Wframe-larger-than=]

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Sumera Priyadarsini <sylphrenadin@gmail.com>
Cc: linux-staging@lists.linux.dev
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210414181129.1628598-8-lee.jones@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>