Fix frame size (stack usage) warning by allocating and freeing
pointers to the data.

drivers/staging/wlan-ng/prism2fw.c:1115:1: warning: the frame size of 4288 bytes is larger than 2048 bytes
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>