Factor out setting the block size. This also contributes to reducing
complexity of function meson_mmc_start_cmd.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>