Although the vSGIs are not directly visible to the host, they still
get moved around by the CPU hotplug, for example. This results in
the kernel moaning on the console, such as:

  genirq: irq_chip GICv4.1-sgi did not update eff. affinity mask of irq 38

Updating the effective affinity on set_affinity() fixes it.
Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>