iio: ad2s1200: Drop legacy include

This driver is using the GPIO descriptor API but yet includes
the legacy <linux/gpio.h> header for no reason. Drop the
surplus include.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/resolver/ad2s1200.c

@@ -10,7 +10,6 @@
 #include <linux/bitops.h>
 #include <linux/delay.h>
 #include <linux/device.h>
-#include <linux/gpio.h>
 #include <linux/gpio/consumer.h>
 #include <linux/module.h>
 #include <linux/mutex.h>