serial: core: Unwrap tertiary assignment in uart_handle_dcd_change()

Prepare for spin lock assertion; move non-trivial assignment into
function body.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_core.c

@@ -2748,12 +2748,15 @@ void uart_handle_dcd_change(struct uart_port *uport, unsigned int status)
 {
 	struct tty_port *port = &uport->state->port;
 	struct tty_struct *tty = port->tty;
-	struct tty_ldisc *ld = tty ? tty_ldisc_ref(tty) : NULL;
+	struct tty_ldisc *ld;
 
-	if (ld) {
-		if (ld->ops->dcd_change)
-			ld->ops->dcd_change(tty, status);
-		tty_ldisc_deref(ld);
+	if (tty) {
+		ld = tty_ldisc_ref(tty);
+		if (ld) {
+			if (ld->ops->dcd_change)
+				ld->ops->dcd_change(tty, status);
+			tty_ldisc_deref(ld);
+		}
 	}
 
 	uport->icount.dcd++;