tty: core: Add helper fn to deref tty driver name

Similar to tty_name(), add tty_driver_name() helper to safely
dereference tty->driver->name (otherwise return empty string).

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 336714c..ef8ee34 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -256,6 +256,13 @@
 
 EXPORT_SYMBOL(tty_name);
 
+const char *tty_driver_name(const struct tty_struct *tty)
+{
+	if (!tty || !tty->driver)
+		return "";
+	return tty->driver->name;
+}
+
 static int tty_paranoia_check(struct tty_struct *tty, struct inode *inode,
 			      const char *routine)
 {