wifi: mwifiex: followup PCIE and related cleanups

Introduce a few more (PCIE and generic interface related)
cleanups which becomes reasonable after the previous patch.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Acked-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230919132804.73340-2-dmantipov@yandex.ru