mmc: meson-gx: remove unneeded configuration bit resets

The variables holding the configuration bits are zero-initialized.
So we can remove all bit resets.

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