Revert "tty/serial: pl011: restrict RX burst FIFO threshold"

This reverts commit f3cb675.

Data loss has been observed on the Pi's PL011 UARTs since f3cb675 was
merged. The loss appears to be on reception, not transmission.

Revert the commit as a workaroud and potential fix.

Link: #6365
Link: #6144 (comment)
Link: https://forums.raspberrypi.com/viewtopic.php?t=376532

Signed-off-by: Phil Elwell <[email protected]>

drivers/tty/serial/amba-pl011.c

@@ -487,12 +487,6 @@ static void pl011_dma_probe(struct uart_amba_port *uap)
 					"RX DMA disabled - no residue processing\n");
 				return;
 			}
-			/*
-			 * DMA controllers with smaller burst capabilities than 1/4
-			 * the FIFO depth will leave more bytes than expected in the
-			 * RX FIFO if mismatched.
-			 */
-			rx_conf.src_maxburst = min(caps.max_burst, rx_conf.src_maxburst);
 		}
 		dmaengine_slave_config(chan, &rx_conf);
 		uap->dmarx.chan = chan;