Documentation: gpio: Replace leading TABs by spaces in code blocks

Code blocks are indented with two spaces. If there's a leading TAB, the
syntax highlighting might be broken in some editors. To prevent that,
unify all code blocks by using spaces instead of leading TAB(s).
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
[Bartosz: tweaked the commit message]
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Documentation/driver-api/gpio/driver.rst

@@ -550,8 +550,8 @@ the interrupt separately and go with it:
   struct my_gpio *g;
   struct gpio_irq_chip *girq;
 
-  ret = devm_request_threaded_irq(dev, irq, NULL,
-		irq_thread_fn, IRQF_ONESHOT, "my-chip", g);
+  ret = devm_request_threaded_irq(dev, irq, NULL, irq_thread_fn,
+                                  IRQF_ONESHOT, "my-chip", g);
   if (ret < 0)
       return ret;