[hardware] Fix masku popc/vfirst tests

hardware/src/masku/masku.sv

@@ -317,12 +317,23 @@ module masku import ara_pkg::*; import rvv_pkg::*; #(
   // Remaining elements of the current instruction in the commit phase
   vlen_t commit_cnt_d, commit_cnt_q;
 
-  // vpopc substitute
-  assign popcount = vcpop_operand[$clog2(DataWidth*NrLanes):0];
+  // Population count for vcpop.m instruction
+  popcount #(
+    .INPUT_WIDTH (DataWidth*NrLanes)
+  ) i_popcount (
+    .data_i    (vcpop_operand),
+    .popcount_o(popcount     )
+  );
 
-  // vfirst substitute
-  assign vfirst_count = vcpop_operand[$clog2(DataWidth*NrLanes)-1:0];
-  assign vfirst_empty = vcpop_operand[0];
+  // Trailing zero counter
+  lzc #(
+    .WIDTH(DataWidth*NrLanes),
+    .MODE (0)
+  ) i_clz (
+    .in_i    (vcpop_operand),
+    .cnt_o   (vfirst_count ),
+    .empty_o (vfirst_empty )
+  );
 
   always_comb begin: p_mask_alu
     alu_result          = '0;