power: supply: smb347-charger: Drop unused include

This driver is including the legacy GPIO header <linux/gpio.h>
but not using any symbols from it. Delete the include.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: David Heidelberg <david@ixit.cz>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>