platform/x86/intel/vsec: Return real error codes from registration path

platform/x86/intel/vsec: Return real error codes from registration path

Stop collapsing registration results into booleans. Make
intel_vsec_walk_header() return int and propagate the first non-zero error
from intel_vsec_register_device(). intel_vsec_register() now returns that
error directly and 0 on success.

This preserves success behavior while surfacing meaningful errors instead
of hiding them behind a bool/-ENODEV, which makes debugging and probe
ordering issues clearer.

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Link: https://patch.msgid.link/20260313015202.3660072-6-david.e.box@linux.intel.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>