wifi: libertas: simplify list operations in free_if_spi_card()

Use 'list_for_each_entry_safe()' to simplify
list operations in 'free_if_spi_card()'.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230725060531.72968-3-dmantipov@yandex.ru