Documentation: gpio: driver.rst: Fix warnings

Fix warnings due to incorrect rst markup. Also improved the presentation
a little without changing the underlying content.
Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
Link: https://lore.kernel.org/r/20191122034702.58563-1-dwlsalmeida@gmail.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/driver-api/gpio/driver.rst

@@ -5,7 +5,7 @@ GPIO Driver Interface
 This document serves as a guide for writers of GPIO chip drivers.
 
 Each GPIO controller driver needs to include the following header, which defines
-the structures used to define a GPIO driver:
+the structures used to define a GPIO driver::
 
 	#include <linux/gpio/driver.h>
 
@@ -398,12 +398,15 @@ provided. A big portion of overhead code will be managed by gpiolib,
 under the assumption that your interrupts are 1-to-1-mapped to the
 GPIO line index:
 
-  GPIO line offset   Hardware IRQ
-  0                  0
-  1                  1
-  2                  2
-  ...                ...
-  ngpio-1            ngpio-1
+.. csv-table::
+    :header: GPIO line offset, Hardware IRQ
+
+    0,0
+    1,1
+    2,2
+    ...,...
+    ngpio-1, ngpio-1
+
 
 If some GPIO lines do not have corresponding IRQs, the bitmask valid_mask
 and the flag need_valid_mask in gpio_irq_chip can be used to mask off some
@@ -413,7 +416,7 @@ The preferred way to set up the helpers is to fill in the
 struct gpio_irq_chip inside struct gpio_chip before adding the gpio_chip.
 If you do this, the additional irq_chip will be set up by gpiolib at the
 same time as setting up the rest of the GPIO functionality. The following
-is a typical example of a cascaded interrupt handler using gpio_irq_chip:
+is a typical example of a cascaded interrupt handler using gpio_irq_chip::
 
 .. code-block:: c
 
@@ -450,7 +453,7 @@ is a typical example of a cascaded interrupt handler using gpio_irq_chip:
   return devm_gpiochip_add_data(dev, &g->gc, g);
 
 The helper support using hierarchical interrupt controllers as well.
-In this case the typical set-up will look like this:
+In this case the typical set-up will look like this::
 
 .. code-block:: c