samples: rust: platform: conditionally call Self::properties_parse()

Only call Self::properties_parse() when the FwNode is an OF node.

Once we add ACPI support, we don't want the ACPI device to fail probing
in Self::properties_parse().

Signed-off-by: Igor Korotin <igor.korotin.linux@gmail.com>
Link: https://lore.kernel.org/r/20250620152103.282763-1-igor.korotin.linux@gmail.com


Signed-off-by: Danilo Krummrich <dakr@kernel.org>