Register tty indexes only for real devices, udev then creates nodes for them
(and only for them).  Move tty_register_driver before probing, to be correct
when calling tty_register_device.  Also tell tty layer by tty_driver flags,
that we are registering devices.

Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>