mmc: meson-gx: rework set_ios function

Remove conditional write of cfg register. Warn if set_clk fails for some
reason. Consistently use host->dev instead of mixing with mmc_dev(mmc)

Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>