leds: tca6507: Include the right header

The TCA6507 optionally presents a GPIO controller, so include
<linux/gpio/driver.h> instead of the legacy <linux/gpio.h>.

Cc: NeilBrown <neilb@suse.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>