staging: r8188eu: Fix sparse warnings in rtw_ieee80211.c

Sparse reports the following:

  CHECK   drivers/staging/rtl8188eu/core/rtw_ieee80211.c
drivers/staging/rtl8188eu/core/rtw_ieee80211.c:1593:14: warning: cast to restricted __le16

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>