device property: fix potential NULL pointer dereference

In device_add_property_set() we check pset parameter for a NULL, but few lines
later we do a pointer arithmetic without check that will crash kernel in the
set_secondary_fwnode().

Here we check if pset parameter is NULL and return immediately.

Fixes: 16ba08d5 (device property: Introduce firmware node type for platform data)
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>