Bluetooth: Use module_platform_driver() in btwilink.c file

module_platform_driver() makes the code simpler by eliminating module_init
and module_exit calls.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>