Bluetooth: hci_intel: add missing tty-device sanity check

Bluetooth: hci_intel: add missing tty-device sanity check

commit dcb9cfaa5ea9aa0ec08aeb92582ccfe3e4c719a9 upstream.

Make sure to check the tty-device pointer before looking up the sibling
platform device to avoid dereferencing a NULL-pointer when the tty is
one end of a Unix98 pty.

Fixes: 74cdad37cd24 ("Bluetooth: hci_intel: Add runtime PM support")
Fixes: 1ab1f239bf17 ("Bluetooth: hci_intel: Add support for platform driver")
Cc: Loic Poulain <loic.poulain@intel.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>