ttydev: fix pamc_zilog for tty pointer move

Today's linux-next build (powerpc allyesconfig) failed like this:

drivers/serial/pmac_zilog.c: In function 'pmz_receive_chars':
drivers/serial/pmac_zilog.c:245: error: 'struct uart_info' has no member named 'tty'
drivers/serial/pmac_zilog.c:250: error: 'struct uart_info' has no member named 'tty'

I applied the patch below (which builds but may, or may not, be correct).
--
Cheers,
Stephen Rothwell                    sfr@canb.auug.org.au
http://www.canb.auug.org.au/~sfr/

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>