mmc: meson-gx: make two functions return void

The return value of meson_mmc_request_done and meson_mmc_read_resp
isn't used, so make both functions return void.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Acked-by: Kevin Hilman <khilman@baylibre.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>