serial: owl: drop low-latency workaround

The owl driver has always carried an unnecessary workaround for the
infamous low_latency behaviour of tty_flip_buffer_push(), which had
been removed years before the driver was added by commit fc60a8b675bd
("tty: serial: owl: Implement console driver").

Specifically, since commit a9c3f68f3cd8 ("tty: Fix low_latency BUG"),
tty_flip_buffer_push() always schedules a work item to push data to the
line discipline and there's no need to keep any low_latency hacks around.

Signed-off-by: Johan Hovold <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/owl-uart.c

···
 		stat = owl_uart_read(port, OWL_UART_STAT);
 	}
 
-	spin_unlock(&port->lock);
 	tty_flip_buffer_push(&port->state->port);
-	spin_lock(&port->lock);
 }
 
 static irqreturn_t owl_uart_irq(int irq, void *dev_id)