tty: serial: fsl_lpuart: Drop unnecessary uart_write_wakeup()

Uart_write_wakeup() will already be called as a part of
lpuart*_transmit_buffer() call, so there doesn't seem to be a reason
to call it again right after.

It also appears that second uart_write_wakeup() might potentially
cause unwanted write wakeup when transmitting an x_char. See commit
5e42e9a3 ("serial: imx: Fix x_char handling and tx flow control")
where this problem was fixed in a very similarly structured i.MX UART
driver.
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Stefan Agner <stefan@agner.ch>
Cc: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Cory Tusar <cory.tusar@zii.aero>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-imx@nxp.com
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Link: https://lore.kernel.org/r/20190729195226.8862-8-andrew.smirnov@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/fsl_lpuart.c

@@ -798,9 +798,6 @@ static void lpuart_txint(struct lpuart_port *sport)
 	else
 		lpuart_transmit_buffer(sport);
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
-		uart_write_wakeup(&sport->port);
-
 out:
 	spin_unlock_irqrestore(&sport->port.lock, flags);
 }