wifi: libertas: cleanup SDIO reset

Embed SDIO reset worker in 'struct if_sdio_card' and so
drop 'reset_host' and 'card_reset_work' static variables,
adjust related code. Not sure whether it's possible to do
something useful on 'mmc_add_host()' error, so just add
'dev_err()' to emit an error message.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230725060531.72968-4-dmantipov@yandex.ru