ath10k: snoc: use module_platform_driver() macro

ath10k_snoc_init()/ath10k_snoc_exit() don't add much value;
module_platform_driver() can remove the boilerplate.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>