KVM: nVMX: Remove stale comment from nested_vmx_load_cr3()

The blurb pertaining to the return value of nested_vmx_load_cr3() no
longer matches reality, remove it entirely as the behavior it is
attempting to document is quite obvious when reading the actual code.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>