mmc: meson-gx: remove mmc host on device removal

The mmc host was added in meson_mmc_probe, but never removed in
meson_mmc_remove.
Fix that by removing the host before deallocating other resources.

Signed-off-by: Michał Zegan <webczat@webczatnet.pl>
Tested-by: Michał Zegan <webczat@webczatnet.pl>
Acked-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>