staging: wlan-ng: add missing byte order conversion

Conversion macros le16_to_cpu was removed and that caused new sparse warning

sparse output:
drivers/staging/wlan-ng/p80211netdev.c:241:44: warning: incorrect type in argument 2 (different base types)
drivers/staging/wlan-ng/p80211netdev.c:241:44:    expected unsigned short [unsigned] [usertype] fc
drivers/staging/wlan-ng/p80211netdev.c:241:44:    got restricted __le16 [usertype] fc

Fixes: 7ad82572 ("staging:wlan-ng:Fix sparse warning")
Signed-off-by: Igor Pylypiv <igor.pylypiv@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>