MIPS: SGI-IP30: Check for valid pointer before using it

Fix issue detected by Smatch:

    ./arch/mips/sgi-ip30/ip30-irq.c:236 heart_domain_free()
     warn: variable dereferenced before check 'irqd' (see line 235)

Fixes: 7505576d ("MIPS: add support for SGI Octane (IP30)")
Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: <stable@vger.kernel.org> # v5.5+

arch/mips/sgi-ip30/ip30-irq.c

@@ -232,9 +232,10 @@ static void heart_domain_free(struct irq_domain *domain,
 		return;
 
 	irqd = irq_domain_get_irq_data(domain, virq);
-	clear_bit(irqd->hwirq, heart_irq_map);
-	if (irqd && irqd->chip_data)
+	if (irqd) {
+		clear_bit(irqd->hwirq, heart_irq_map);
 		kfree(irqd->chip_data);
+	}
 }
 
 static const struct irq_domain_ops heart_domain_ops = {