HID: fix memory leak in hidraw_release

hidraw_release() forgot to free the linked list structure, causing memory
leak.
Reported-by: Juan Marcos Diez Esteban <juan_m_diez@yahoo.es>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hidraw.c

@@ -211,6 +211,8 @@ static int hidraw_release(struct inode * inode, struct file * file)
 			kfree(list->hidraw);
 	}
 
+	kfree(list);
+
 	return 0;
 }