Revert "serial: omap: unlock the port lock"

This reverts commit 0324a821.

That commit tried to fix a deadlock problem when using
hci_ldisc, but it turns out the bug was in hci_ldsic
all along where it was calling ->write() from within
->write_wakeup() callback.

The problem is that ->write_wakeup() was called with
port lock held and ->write() tried to grab the same
port lock.
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/omap-serial.c

@@ -398,11 +398,8 @@ static void transmit_chars(struct uart_omap_port *up, unsigned int lsr)
 			break;
 	} while (--count > 0);
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS) {
-		spin_unlock(&up->port.lock);
+	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
 		uart_write_wakeup(&up->port);
-		spin_lock(&up->port.lock);
-	}
 
 	if (uart_circ_empty(xmit))
 		serial_omap_stop_tx(&up->port);