KVM: x86/mmu: Fix kdoc of __handle_changed_spte

The function name of kdoc of __handle_changed_spte() should be itself,
rather than handle_changed_spte().  Fix the typo.

Signed-off-by: Kai Huang <kai.huang@intel.com>
Message-Id: <20210503042446.154695-1-kai.huang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>