[dv] Fix u_rst_shadow_cnt behavior in testbench

Two fixes:
- When `LockstepOffset = 1`, the `u_rst_shadow_cnt` instance does not
  exist.
- Fix the `u_rst_shadow_cnt` instance path as it is now in
  `gen_reset_counter`.

Signed-off-by: Pascal Nasahl <nasahlpa@lowrisc.org>

Author: nasahlpa

dv/uvm/core_ibex/tb/core_ibex_tb_top.sv

@@ -379,9 +379,10 @@ module core_ibex_tb_top;
   end
 
   // Manually set unused_assert_connected = 1 to disable the AssertConnected_A assertion for
-  // prim_count in case lockstep (set by SecureIbex) is enabled. If not disabled, DV fails.
-  if (SecureIbex) begin : gen_disable_count_check
-    assign dut.u_ibex_top.gen_lockstep.u_ibex_lockstep.u_rst_shadow_cnt.
+  // prim_count in case lockstep (set by SecureIbex) is enabled and the lockstep offset is
+  // larger than 1. If not disabled, DV fails.
+  if (SecureIbex && LockstepOffset > 1) begin : gen_disable_count_check
+    assign dut.u_ibex_top.gen_lockstep.u_ibex_lockstep.gen_reset_counter.u_rst_shadow_cnt.
           unused_assert_connected = 1;
   end