serial: core: Remove extra locking in uart_write()

uart_start() only claims the port->lock to call __uart_start(),
which does the actual processing. Eliminate the extra acquire/release
in uart_write(); call __uart_start() directly with port->lock already
held.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_core.c

@@ -537,9 +537,10 @@ static int uart_write(struct tty_struct *tty,
 		count -= c;
 		ret += c;
 	}
+
+	__uart_start(tty);
 	spin_unlock_irqrestore(&port->lock, flags);
 
-	uart_start(tty);
 	return ret;
 }