gpio: mockup: use simple_read_from_buffer() in debugfs read callback

Calling read() for a single byte read will return 2 currently. Use
simple_read_from_buffer() which correctly handles all sizes.

Fixes: 2a9e2740 ("gpio: mockup: rework debugfs interface")
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpio-mockup.c

@@ -204,10 +204,9 @@ static ssize_t gpio_mockup_debugfs_read(struct file *file,
 	struct gpio_mockup_chip *chip;
 	struct seq_file *sfile;
 	struct gpio_chip *gc;
-	int val, rv, cnt;
+	int val, cnt;
 	char buf[3];
 
-
 	if (*ppos != 0)
 		return 0;
 
@@ -219,12 +218,7 @@ static ssize_t gpio_mockup_debugfs_read(struct file *file,
 	val = gpio_mockup_get(gc, priv->offset);
 	cnt = snprintf(buf, sizeof(buf), "%d\n", val);
 
-	rv = copy_to_user(usr_buf, buf, cnt);
-	if (rv)
-		return rv;
-
-	*ppos += cnt;
-	return cnt;
+	return simple_read_from_buffer(usr_buf, size, ppos, buf, cnt);
 }
 
 static ssize_t gpio_mockup_debugfs_write(struct file *file,