pc300: Update to tty_set_operations

This driver somehow escaped the tty operations changes way back when.  Update
it so that we can switch to tty->ops shortly.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>