serial: meson: drop low-latency workaround

The meson driver has always carried an unnecessary workaround for the
infamous low_latency behaviour of tty_flip_buffer_push(), which had
already been removed by the time the driver was added by commit
ff7693d0 ("ARM: meson: serial: add MesonX SoC on-chip uart driver").

Specifically, since commit a9c3f68f ("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: NJohan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210421095509.3024-15-johan@kernel.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/meson_uart.c

@@ -226,9 +226,7 @@ static void meson_receive_chars(struct uart_port *port)
 
 	} while (!(readl(port->membase + AML_UART_STATUS) & AML_UART_RX_EMPTY));
 
-	spin_unlock(&port->lock);
 	tty_flip_buffer_push(tport);
-	spin_lock(&port->lock);
 }
 
 static irqreturn_t meson_uart_interrupt(int irq, void *dev_id)