Revert "serial: core: only stop transmit when HW fifo is empty"

This reverts commit 7bfb915.

This commit broke pxa and omap-serial, because it inhibited them from
calling stop_tx() if their TX FIFOs weren't completely empty. This
resulted in these two drivers hanging during transmits because the TX
interrupt would stay enabled, and a new TX interrupt would never fire.

Cc: stable@vger.kernel.org
Fixes: 7bfb915 ("serial: core: only stop transmit when HW fifo is empty")
Signed-off-by: Doug Brown <doug@schmorgal.com>
Link: https://lore.kernel.org/r/20240606195632.173255-2-doug@schmorgal.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: dougg3

include/linux/serial_core.h

@@ -811,8 +811,7 @@ enum UART_TX_FLAGS {
 	if (pending < WAKEUP_CHARS) {					      \
 		uart_write_wakeup(__port);				      \
 									      \
-		if (!((flags) & UART_TX_NOSTOP) && pending == 0 &&	      \
-		    __port->ops->tx_empty(__port))			      \
+		if (!((flags) & UART_TX_NOSTOP) && pending == 0)	      \
 			__port->ops->stop_tx(__port);			      \
 	}								      \
 									      \