irqchip/gic-v3-its: Free unused vpt_page when alloc vpe table fail

In its_vpe_init, when its_alloc_vpe_table fails, we should free
vpt_page allocated just before, instead of vpe->vpt_page.
Let's fix it.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Nianyao Tang <tangnianyao@huawei.com>
Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>