staging: r8188eu: Fix sparse warning in core/rtw_xmit.c

Sparse reports the following warning:

  CHECK   drivers/staging/rtl8188eu/core/rtw_xmit.c
drivers/staging/rtl8188eu/core/rtw_xmit.c:809:23: warning: incorrect type in initializer (different base types)
drivers/staging/rtl8188eu/core/rtw_xmit.c:809:23:    expected unsigned short [usertype] *fctrl
drivers/staging/rtl8188eu/core/rtw_xmit.c:809:23:    got restricted __le16 *<noident>

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