wifi: brcmsmac: Drop legacy header

The driver is using all the modern abstractions to obtain and use
GPIOs and the legacy <linux/gpio.h> header is unused, so drop it.

Fixes: a8e59744 ("gpiolib: split linux/gpio/driver.h out of linux/gpio.h")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20240131-descriptors-wireless-v1-3-e1c7c5d68746@linaro.org