pinctrl: st: Include the right header

The ST pinctrl driver wants to provode a gpio_chip but is not
including the header for this, fix the inclusion to use the right
header. <linux/of_gpio.h> has to remain as the driver is calling
of_get_named_gpio().

Cc: Patrice Chotard <patrice.chotard@st.com>
Cc: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20190820111135.10701-1-linus.walleij@linaro.org

drivers/pinctrl/pinctrl-st.c

@@ -12,8 +12,9 @@
 #include <linux/io.h>
 #include <linux/of.h>
 #include <linux/of_irq.h>
-#include <linux/of_gpio.h>
+#include <linux/of_gpio.h> /* of_get_named_gpio() */
 #include <linux/of_address.h>
+#include <linux/gpio/driver.h>
 #include <linux/regmap.h>
 #include <linux/mfd/syscon.h>
 #include <linux/pinctrl/pinctrl.h>