snowball: Clear UART RX FIFO

Without usb-serial cable plugged at this stage, some
garbage is seen in UART RX FIFO, which blocks autoboot
progress. The fix makes sure to empty the RX FIFO,
before we wait for user input to interrupt autoboot.

Signed-off-by: Ramesh Chandrasekaran <ramesh.chandrasekaran@stericsson.com>

board/st-ericsson/snowball/snowball.c

@@ -253,6 +253,10 @@ int board_late_init(void)
 	if ((raise_ab8500_gpio16() < 0))
 		printf("error: cant' raise GPIO16\n");
 
+	/* empty UART RX FIFO */
+	while (tstc())
+		(void) getc();
+
 	return 0;
 }