KVM: arm64: Constify kvm_io_gic_ops

The only usage of kvm_io_gic_ops is to make a comparison with its
address and to pass its address to kvm_iodevice_init() which takes a
pointer to const kvm_io_device_ops as input. Make it const to allow the
compiler to put it in read-only memory.

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211204213518.83642-1-rikard.falkeborn@gmail.com