Refactor interface of microkernel parameter initialization

Pass pointer to the parameters structure to enable polymorphic extensions

PiperOrigin-RevId: 374147239
diff --git a/bench/f32-vsqrt.cc b/bench/f32-vsqrt.cc
index a85f279..36e5cb5 100644
--- a/bench/f32-vsqrt.cc
+++ b/bench/f32-vsqrt.cc
@@ -38,7 +38,8 @@
   std::generate(input.begin(), input.end(), std::ref(f32rng));
   std::fill(output.begin(), output.end(), std::nanf(""));
 
-  const union xnn_f32_sqrt_params params = xnn_init_f32_sqrt_params();
+  union xnn_f32_sqrt_params params;
+  xnn_init_f32_sqrt_params(&params);
   for (auto _ : state) {
     vsqrt(elements * sizeof(float), input.data(), output.data(), &params);
   }