[SERIAL] 8250 serial console update uart_8250_port ier

On some embedded PowerPC (MPC834x) systems an extra byte would some
times be required to flush data out of the fifo.
serial8250_console_write() was updating the IER in hardware without
also updating the copy in uart_8250_port. This causes issues functions
like serial8250_start_tx() and __stop_tx() to misbehave.
Signed-off-by: NKumar Gala <galak@kernel.crashing.org>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

drivers/serial/8250.c

@@ -2229,6 +2229,7 @@ serial8250_console_write(struct console *co, const char *s, unsigned int count)
 	 *	and restore the IER
 	 */
 	wait_for_xmitr(up, BOTH_EMPTY);
+	up->ier |= UART_IER_THRI;
 	serial_out(up, UART_IER, ier | UART_IER_THRI);
 }