KVM: arm64: Fix documentation for vgic_its_iter_next()

As reported by the build robot, the documentation for vgic_its_iter_next()
contains a typo. Fix it.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202505221421.KAuWlmSr-lkp@intel.com/


Signed-off-by: Marc Zyngier <maz@kernel.org>