net: dsa: mt7530: Drop unused GPIO include

This driver uses GPIO descriptors only, <linux/of_gpio.h>
is not used so drop the include.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>