staging wlan-ng: fix type mismatch warnings in mkpdrlist()

struct  hfa384x_pdrec len and code fields as clearly little endian,
mark both fields as such. pda->buf is also clearly little endian.

Fixes sparse warnings:

  drivers/staging/wlan-ng/prism2fw.c:613:16: warning: cast to restricted __le16
  drivers/staging/wlan-ng/prism2fw.c:616:21: warning: cast to restricted __le16
  drivers/staging/wlan-ng/prism2fw.c:625:21: warning: cast to restricted __le16

Signed-off-by: Maciek Borzecki <maciek.borzecki@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>