extcon: usb-gpio: Use the right includes

The USB GPIO extcon driver does not use any of the legacy
includes <linux/gpio.h> or <linux/of_gpio.h> but
exploits the fact that this brings in <linux/mod_device_table.h>.
Fix this up by using the right includes.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>