I've been hitting a crash on boot where tty_open is being called before the
hvc console driver setup is complete.  This fixes the problem.

Thanks to benh for his help on this.
Signed-off-by: Michael Neuling <mikey@neuling.org>
Acked-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>