docs: driver-api: gpio: consumer: Mark another line of code as such

Make it so that this #include line is rendered in monospace, like other
code blocks.
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

Documentation/driver-api/gpio/consumer.rst

@@ -12,7 +12,7 @@ Guidelines for GPIOs consumers
 
 Drivers that can't work without standard GPIO calls should have Kconfig entries
 that depend on GPIOLIB or select GPIOLIB. The functions that allow a driver to
-obtain and use GPIOs are available by including the following file:
+obtain and use GPIOs are available by including the following file::
 
 	#include <linux/gpio/consumer.h>