spapr: Add return value to spapr_irq_check()

spapr: Add return value to spapr_irq_check()

Explicitly return success or failure, rather than just relying on the
Error ** parameter.  This makes handling it less verbose in the caller.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>