platform/x86: intel_cht_int33fe: Remove duplicate NULL check

Since i2c_unregister_device() became NULL-aware we may remove duplicate
NULL check.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>