iio: atlas-ph-sensor: Drop GPIO include

The driver includes <linux/gpio.h> yet fails to use symbols
from any the header so drop the include.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Matt Ranostay <matt.ranostay@konsulko.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/chemical/atlas-ph-sensor.c

@@ -14,7 +14,6 @@
 #include <linux/err.h>
 #include <linux/irq.h>
 #include <linux/irq_work.h>
-#include <linux/gpio.h>
 #include <linux/i2c.h>
 #include <linux/of_device.h>
 #include <linux/regmap.h>