dev->dev.platform_data is optional and not guaranteed to be set by the platform device registrar. Add a NULL guard and return -EINVAL to fail the probe cleanly instead of crashing the kernel with a NULL dereference.

Summary by cubic

Add a NULL check for platform_data in devicemodel_probe to prevent a NULL dereference and kernel crash. If platform data is missing, log an error and return -EINVAL to fail the probe cleanly.

^{Written for commit 1d3a336. Summary will update on new commits.}