serial: amba-pl010: drop low-latency workaround

Commit 2389b272168c ("[ARM] 4417/1: Serial: Fix AMBA drivers locking")
worked around the infamous low_latency behaviour of
tty_flip_buffer_push() by simply dropping and reacquiring the port lock
in the interrupt handler.

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.

Cc: Russell King <[e-mail]>
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/amba-pl010.c

···
 	ignore_char:
 		status = readb(uap->port.membase + UART01x_FR);
 	}
-	spin_unlock(&uap->port.lock);
 	tty_flip_buffer_push(&uap->port.state->port);
-	spin_lock(&uap->port.lock);
 }
 
 static void pl010_tx_chars(struct uart_amba_port *uap)