gpio: No need to cast away return value of debugfs_create_file()

It is fine to ignore the return value (and encouraged), so need to cast
away the return value, you will not get a build warning at all.

Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc: linux-gpio@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -4802,8 +4802,8 @@ static const struct file_operations gpiolib_operations = {
 static int __init gpiolib_debugfs_init(void)
 {
 	/* /sys/kernel/debug/gpio */
-	(void) debugfs_create_file("gpio", S_IFREG | S_IRUGO,
-				NULL, NULL, &gpiolib_operations);
+	debugfs_create_file("gpio", S_IFREG | S_IRUGO, NULL, NULL,
+			    &gpiolib_operations);
 	return 0;
 }
 subsys_initcall(gpiolib_debugfs_init);