Bluetooth: mediatek: Use module_sdio_driver helper

Macro module_sdio_driver is used for drivers whose init and exit paths
only register and unregister to SDIO API. So remove boilerplate code to
make code simpler by using module_sdio_driver.

Suggested-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>