irqchip/gic-v3-its: Gracefully fail on LPI exhaustion

[ Upstream commit 45725e0fc3e7fe52fedb94f59806ec50e9618682 ]

In the unlikely event that we cannot find any available LPI in the
system, we should gracefully return an error instead of carrying
on with no LPI allocated at all.

Fixes: 38dd7c49 ("irqchip/gic-v3-its: Drop chunk allocation compatibility")
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>

drivers/irqchip/irq-gic-v3-its.c

@@ -1581,6 +1581,9 @@ static unsigned long *its_lpi_alloc(int nr_irqs, u32 *base, int *nr_ids)
 		nr_irqs /= 2;
 	} while (nr_irqs > 0);
 
+	if (!nr_irqs)
+		err = -ENOSPC;
+
 	if (err)
 		goto out;