gpio: mockup: return -EFAULT if copy_from_user() fails

copy_from_user() returns the number of bytes remaining to be copied but
we want to return negative error codes on failue.

Fixes: 9202ba2397d1 ("gpio: mockup: implement event injecting over debugfs")
Signed-off-by: Dan Carpenter <[e-mail]>
Acked-by: Bartosz Golaszewski <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

drivers/gpio/gpio-mockup.c

···
 	struct seq_file *sfile;
 	struct gpio_desc *desc;
 	struct gpio_chip *gc;
-	int status, val;
+	int val;
 	char buf;
 
 	sfile = file->private_data;
···
 	chip = priv->chip;
 	gc = &chip->gc;
 
-	status = copy_from_user(&buf, usr_buf, 1);
-	if (status)
-		return status;
+	if (copy_from_user(&buf, usr_buf, 1))
+		return -EFAULT;
 
 	if (buf == '0')
 		val = 0;