Bitnet: trying an alternative iq1_bn grid

Faster on CUDA. The scalar version is faster too.
The issue with CUDA is that now I see wild performance
fluctuations. Running llama-bench I can get 220 t/s
for TG-128 one time, and 190 t/s another time, with
uncertaintiers of 1-2 t/s. Same for PP, results are
jumping back-and-fort between ~9500 t/s and ~8900 t/s.
So, basically no reliable measurement at this point,
but for sure faster than the previous version, which was
at around 170-180 t/s.

iqk_mul_mat.cpp

@@ -2788,6 +2788,7 @@ bool MulMat::prepare(int typeA, int typeB, int ne00, MulMat& mm, int Ny) {
             MulMat::set_functions<DequantizerIQ2XXS>(mm);
             break;
         case GGML_TYPE_IQ1_BN:
+            return false;
             assert (ne00 % QK_IQ1BN == 0);
             mm.funcs[0] = mul_mat_iq1bn_q8_K64<1>;
             mm.funcs[1] = mul_mat_iq1bn_q8_K64<2>;