KVM: nVMX: KVM_SET_NESTED_STATE - Tear down old EVMCS state before setting new state

Move call to nested_enable_evmcs until after free_nested() is complete.

Signed-off-by: Aaron Lewis <aaronlewis@google.com>
Reviewed-by: Marc Orr <marcorr@google.com>
Reviewed-by: Peter Shier <pshier@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>