soc: mediatek: mtk-mutex: Use module_platform_driver() macro

Replace open-coded init/exit calls with the module_platform_driver()
macro being equivalent.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20230222094253.23678-8-angelogioacchino.delregno@collabora.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>