serial: trim locking on the helpers

The port mutex protects port->tty, but these paths never need to walk from
port->tty. They do need the low level lock as the API expects that but they
already also take it.

Thus we can drop the extra mutex lock calls here.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/serial/serial_core.c

@@ -1506,12 +1506,10 @@ static int uart_carrier_raised(struct tty_port *port)
 	struct uart_state *state = container_of(port, struct uart_state, port);
 	struct uart_port *uport = state->uart_port;
 	int mctrl;
-	mutex_lock(&port->mutex);
 	spin_lock_irq(&uport->lock);
 	uport->ops->enable_ms(uport);
 	mctrl = uport->ops->get_mctrl(uport);
 	spin_unlock_irq(&uport->lock);
-	mutex_unlock(&port->mutex);
 	if (mctrl & TIOCM_CAR)
 		return 1;
 	return 0;
@@ -1521,12 +1519,11 @@ static void uart_dtr_rts(struct tty_port *port, int onoff)
 {
 	struct uart_state *state = container_of(port, struct uart_state, port);
 	struct uart_port *uport = state->uart_port;
-	mutex_lock(&port->mutex);
+
 	if (onoff)
 		uart_set_mctrl(uport, TIOCM_DTR | TIOCM_RTS);
 	else
 		uart_clear_mctrl(uport, TIOCM_DTR | TIOCM_RTS);
-	mutex_unlock(&port->mutex);
 }
 
 /*