Fix for "serial: 8250: Toggle IER bits on only after irq has been setup"

JIRA: INTERNAL
Upstream Status: RHEL only

This patch somehow added the same code that was already there, removing
the offending patch.

Signed-off-by: Lucas Zampieri <lzampier@redhat.com>

Author: zampierilucas

drivers/tty/serial/8250/8250_port.c

@@ -2334,10 +2334,6 @@ int serial8250_do_startup(struct uart_port *port)
 	if (retval)
 		goto out;
 
-	retval = up->ops->setup_irq(up);
-	if (retval)
-		goto out;
-
 	if (port->irq && !(up->port.flags & UPF_NO_THRE_TEST)) {
 		unsigned char iir1;