Edwards map fix

ECCKiila Changes from

https://gitlab.com/nisec/ecckiila/-/issues/2

https://gitlab.com/nisec/ecckiila/-/commit/7445ecabef77965743e0ae8d39d7433b07820be6

* X3 -> X1
* eliminate a temp variable

X3 = X1 as pointers is the reason this was still passing unit tests.
But that might not hold in future versions of ECCKiila, so fix it now.

(cherry picked from commit 259301a5)