ARM: PL011: Ensure error flags are clear at startup

The error flags weren't being cleared upon UART startup, which
can cause problems when we add DMA support.  It's good practice
to ensure that these flags are cleared anyway, so let's do so.

This was part of a larger patch from Linus Walleij.

Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

drivers/serial/amba-pl011.c

@@ -424,6 +424,10 @@ static int pl011_startup(struct uart_port *port)
 	cr = UART01x_CR_UARTEN | UART011_CR_RXE | UART011_CR_TXE;
 	writew(cr, uap->port.membase + UART011_CR);
 
+	/* Clear pending error interrupts */
+	writew(UART011_OEIS | UART011_BEIS | UART011_PEIS | UART011_FEIS,
+	       uap->port.membase + UART011_ICR);
+
 	/*
 	 * initialise the old status of the modem signals
 	 */