tty: serial: 8250: add CON_CONSDEV to flags

When using the 8250 as a boot console and the main console results in
messages being printed twice.  The console framework will only
unregister boot consoles if a new console is registered with the
CON_CONSDEV flag set.

Set this flag for the univ8250 console to prevent double-registration.
Signed-off-by: NMatthew Leach <matthew.leach@codethink.co.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_core.c

@@ -675,7 +675,7 @@ static struct console univ8250_console = {
 	.device		= uart_console_device,
 	.setup		= univ8250_console_setup,
 	.match		= univ8250_console_match,
-	.flags		= CON_PRINTBUFFER | CON_ANYTIME,
+	.flags		= CON_PRINTBUFFER | CON_ANYTIME | CON_CONSDEV,
 	.index		= -1,
 	.data		= &serial8250_reg,
 };