Add missing call to uart_update_timeout()

This patch fixes a problem reported here:
http://article.gmane.org/gmane.linux.ports.arm.kernel/155242/match=auart



Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>