irqdomain: Drop bogus fwspec-mapping error handling

In case a newly allocated IRQ ever ends up not having any associated
struct irq_data it would not even be possible to dispose the mapping.

Replace the bogus disposal with a WARN_ON().

This will also be used to fix a shared-interrupt mapping race, hence the
CC-stable tag.

Fixes: 1e2a7d78 ("irqdomain: Don't set type when mapping an IRQ")
Cc: stable@vger.kernel.org      # 4.8
Tested-by: Hsin-Yi Wang <hsinyi@chromium.org>
Tested-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230213104302.17307-4-johan+linaro@kernel.org

kernel/irq/irqdomain.c

@@ -847,13 +847,8 @@ unsigned int irq_create_fwspec_mapping(struct irq_fwspec *fwspec)
 	}
 
 	irq_data = irq_get_irq_data(virq);
-	if (!irq_data) {
-		if (irq_domain_is_hierarchy(domain))
-			irq_domain_free_irqs(virq, 1);
-		else
-			irq_dispose_mapping(virq);
+	if (WARN_ON(!irq_data))
 		return 0;
-	}
 
 	/* Store trigger type */
 	irqd_set_trigger_type(irq_data, type);