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: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>