serial: fix serial_txx9.c build warning/typo

Fix kconfig symbol test to use "defined":

drivers/tty/serial/serial_txx9.c: warning: "CONFIG_CONSOLE_POLL" is not defined [-Wundef]
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_txx9.c

@@ -466,7 +466,7 @@ static void serial_txx9_break_ctl(struct uart_port *port, int break_state)
 	spin_unlock_irqrestore(&up->port.lock, flags);
 }
 
-#if defined(CONFIG_SERIAL_TXX9_CONSOLE) || (CONFIG_CONSOLE_POLL)
+#if defined(CONFIG_SERIAL_TXX9_CONSOLE) || defined(CONFIG_CONSOLE_POLL)
 /*
  *	Wait for transmitter & holding register to empty
  */