[PATCH] Serial: Adjust serial locking

This patch changes the way serial ports are locked when getting modem
status.  This change is necessary because we will need to atomically
read the modem status and take action depending on the CTS status.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

Documentation/serial/driver

@@ -107,8 +107,8 @@ hardware.
 	indicate that the signal is permanently active.  If RI is
 	not available, the signal should not be indicated as active.
 
-	Locking: none.
-	Interrupts: caller dependent.
+	Locking: port->lock taken.
+	Interrupts: locally disabled.
 	This call must not sleep
 
   stop_tx(port,tty_stop)