KVM: nVMX: Fix size checks in vmx_set_nested_state

The size checks in vmx_nested_state are wrong because the calculations
are made based on the size of a pointer to a struct kvm_nested_state
rather than the size of a struct kvm_nested_state.

Reported-by: Felix Wilhelm <fwilhelm@google.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Drew Schmitt <dasch@google.com>
Reviewed-by: Marc Orr <marcorr@google.com>
Reviewed-by: Peter Shier <pshier@google.com>
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Fixes: 8fcc4b59
Cc: stable@ver.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>