irqchip/gic-v5: Remove the redundant ITS cache invalidation

An ITS cache invalidation has been performed immediately after programming
the L2 DTE in gicv5_its_device_register(). No need to perform it again
right after a successful gicv5_its_device_register().

Remove it.

Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/all/20250903023319.1820-1-yuzenghui@huawei.com