irqchip/gic-v3-its: Remove BUG_ON in its_vpe_irq_domain_alloc

This BUG_ON() is useless, because the same effect will be obtained 
by letting the code run its course and vm being dereferenced,
triggering an exception.

So just remove this check.
Signed-off-by: Guanrui Huang <guanrui.huang@linux.alibaba.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240418061053.96803-3-guanrui.huang@linux.alibaba.com

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

@@ -4526,8 +4526,6 @@ static int its_vpe_irq_domain_alloc(struct irq_domain *domain, unsigned int virq
 	struct page *vprop_page;
 	int base, nr_ids, i, err = 0;
 
-	BUG_ON(!vm);
-
 	bitmap = its_lpi_alloc(roundup_pow_of_two(nr_irqs), &base, &nr_ids);
 	if (!bitmap)
 		return -ENOMEM;