tty: serial: fsl_lpuart: Fix lpuart_flush_buffer()

Fix incorrect read-modify-write sequence in lpuart_flush_buffer() that
was reading from UARTPFIFO and writing to UARTCFIFO instead of
operating solely on the latter.

Fixes: 9bc19af ("tty: serial: fsl_lpuart: Flush HW FIFOs in .flush_buffer")
Signed-off-by: Andrey Smirnov <[email protected]>
Reported-by: Vivien Didelot <[email protected]>
Tested-by: Vivien Didelot <[email protected]>
Tested-by: Andrew Lunn <[email protected]>
Reviewed-by: Fabio Estevam <[email protected]>
Cc: Stefan Agner <[email protected]>
Cc: Chris Healy <[email protected]>
Cc: Cory Tusar <[email protected]>
Cc: Lucas Stach <[email protected]>
Cc: Jiri Slaby <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: ndreys

drivers/tty/serial/fsl_lpuart.c

@@ -548,7 +548,7 @@ static void lpuart_flush_buffer(struct uart_port *port)
 		val |= UARTFIFO_TXFLUSH | UARTFIFO_RXFLUSH;
 		lpuart32_write(&sport->port, val, UARTFIFO);
 	} else {
-		val = readb(sport->port.membase + UARTPFIFO);
+		val = readb(sport->port.membase + UARTCFIFO);
 		val |= UARTCFIFO_TXFLUSH | UARTCFIFO_RXFLUSH;
 		writeb(val, sport->port.membase + UARTCFIFO);
 	}