staging:r8188eu: remove unused HW_VAR_RF_TYPE parameter of HT_caps_handler

rtw_hal_get_hwreg() does not used with HW_VAR_RF_TYPE parameter.
Remove HW_VAR_RF_TYPE switch case in rtw_hal_get_hwreg and definition.

Signed-off-by: Ivan Safonov <insafonov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>