gpiolib: use gpiochip_get_desc() in gpio_ioctl()

Unduplicate the offset check by simply calling gpiochip_get_desc() and
checking its return value.
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -1175,10 +1175,11 @@ static long gpio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 
 		if (copy_from_user(&lineinfo, ip, sizeof(lineinfo)))
 			return -EFAULT;
-		if (lineinfo.line_offset >= gdev->ngpio)
-			return -EINVAL;
 
-		desc = &gdev->descs[lineinfo.line_offset];
+		desc = gpiochip_get_desc(chip, lineinfo.line_offset);
+		if (IS_ERR(desc))
+			return PTR_ERR(desc);
+
 		if (desc->name) {
 			strncpy(lineinfo.name, desc->name,
 				sizeof(lineinfo.name));