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

This reverts commit 2dc559c.

drivers/tty/serial/amba-pl011.c

@@ -487,6 +487,12 @@ 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;