device property: Document how to check for the property presence

device property: Document how to check for the property presence

Currently it's unclear if one may or may not rely on the error codes
returned from the property getters to check for the property presence.
Clarify this by updating kernel-doc for fwnode_property_*() and
device_property_*() where it's applicable.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/r/4b24f1f4-b395-467a-81b7-1334a2d48845@roeck-us.net
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Link: https://patch.msgid.link/20260318142404.2526642-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>