staging: r8188eu: remove dead code from rtw_get_cur_max_rate function

Values assugned to pht_capie and mcs_rate variables,
but variables does not used.

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