migration: make loadvm_postcopy_handle_resume() void

migration: make loadvm_postcopy_handle_resume() void

This is an incremental step in converting vmstate loading
code to report error via Error objects instead of directly
printing it to console/monitor.

Use warn_report() instead of error_report(); it ensures that
a resume command received while the migration is not
in postcopy recover state is not fatal. It only informs that
the command received is unusual, and therefore we should not set
errp with the error string.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Arun Menon <armenon@redhat.com>
Tested-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Link: https://lore.kernel.org/r/20250918-propagate_tpm_error-v14-13-36f11a6fb9d3@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>