mmc: meson-gx: minor improvements in meson_mmc_set_ios

mmc: meson-gx: minor improvements in meson_mmc_set_ios

val isn't used in the switch clause and afterwards there's an
identical statement. So remove it.

In case of an unexpected bus width the error message indicates
the intention to set the bus width to 4 and to go on.
So remove the return statement. This return statement also
conflicts with "setting to 4" because nothing would be set
actually before returning. 4bit bus width are chosen as
default as the vendor driver does it too.

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