Make sure to set the tty class-device driver data before registering the
tty to avoid having a racing open() dereference a NULL pointer.

Fixes: 91ca10d6 ("misc: bcm-vk: add ttyVK support")
Cc: stable@vger.kernel.org      # 5.12
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210917115736.5816-1-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>