irqchip/gic-v3-its: Reference to its_invall_cmd descriptor when building INVALL

[ Upstream commit 10794522 ]

It looks like an obvious mistake to use its_mapc_cmd descriptor when
building the INVALL command block. It so far worked by luck because
both its_mapc_cmd.col and its_invall_cmd.col sit at the same offset of
the ITS command descriptor, but we should not rely on it.

Fixes: cc2d3216

 ("irqchip: GICv3: ITS command queue")
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20191202071021.1251-1-yuzenghui@huawei.com
Signed-off-by: Sasha Levin <sashal@kernel.org>