mmc: sunxi: Removing unused code

Removing a relict from reverse engineering of the Android driver code
in sunxi_mmc_clk_set_rate.

Signed-off-by: David Lanzendörfer <david.lanzendoerfer@o2s.ch>
Reported-by: <lixiang@allwinnertech.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>