serial: omap: make sure to put() on poll_get_char

if we would reach serial_omap_get_char() while
Data Ready bit isn't set, we would return from
it without kicking our pm timer. This would mean
we would, eventually, have an unbalanced
pm_runtime_get on our device which would prevent
it from ever sleeping again.
Tested-by: NShubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/omap-serial.c

@@ -1005,12 +1005,17 @@ static int serial_omap_poll_get_char(struct uart_port *port)
 
 	pm_runtime_get_sync(up->dev);
 	status = serial_in(up, UART_LSR);
-	if (!(status & UART_LSR_DR))
-		return NO_POLL_CHAR;
+	if (!(status & UART_LSR_DR)) {
+		status = NO_POLL_CHAR;
+		goto out;
+	}
 
 	status = serial_in(up, UART_RX);
+
+out:
 	pm_runtime_mark_last_busy(up->dev);
 	pm_runtime_put_autosuspend(up->dev);
+
 	return status;
 }