wifi: brcmsmac: remove unused data type

Remove unused 'struct gpioh_item'. It seems it was so since
commit 5b435de0 ("net: wireless: add brcm80211 drivers").

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230719083232.158177-1-dmantipov@yandex.ru