cad/openvsp: fix build on powerpc64

/wrkdirs/usr/ports/cad/openvsp/work/.build/Libraries-prefix/src/Libraries-build/EIGEN-prefix/src/EIGEN/Eigen/src/Core/arch/AltiVec/PacketMath.h:1340:32: error: use of undeclared identifier 'vec_sqrt'; did you mean 'vec_rsqrte'?
  BF16_TO_F32_UNARY_OP_WRAPPER(vec_sqrt, a);