tty: fix tty_port_block_til_ready waiting

Since commit 3e3b5c08

 ("tty: use
prepare/finish_wait"), tty_port_block_til_ready() is using
prepare_to_wait()/finish_wait().  Those functions require that the
wait_queue_t be initialised with .func=autoremove_wake_function, via
DEFINE_WAIT().

But the conversion from DECLARE_WAITQUEUE() to DEFINE_WAIT() was not made,
so this code will oops in finish_wait().

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>