Firmware: firmware_class, fix lock imbalance

Add omitted unlock in firmware_data_read.
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/firmware_class.c

@@ -217,8 +217,10 @@ firmware_data_read(struct kobject *kobj, struct bin_attribute *bin_attr,
 		ret_count = -ENODEV;
 		goto out;
 	}
-	if (offset > fw->size)
-		return 0;
+	if (offset > fw->size) {
+		ret_count = 0;
+		goto out;
+	}
 	if (count > fw->size - offset)
 		count = fw->size - offset;