mmc: meson-gx: use devm_mmc_alloc_host

Use new function devm_mmc_alloc_host() to simplify the code.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/728f159b-885f-c78a-1a3d-f55c245250e1@gmail.com


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