mmc: meson-gx: switch to device-managed dmam_alloc_coherent()

Using the device-managed version allows to simplify clean-up in probe()
error path and remove().

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/268b3cd5-2388-2553-bdba-c72853f91aa3@gmail.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>