[prim_subreg_shadow] Make local parameter a localparam

Signed-off-by: Philipp Wagner <phw@lowrisc.org>

hw/ip/prim/rtl/prim_subreg_shadow.sv

diff --git a/hw/ip/prim/rtl/prim_subreg_shadow.sv b/hw/ip/prim/rtl/prim_subreg_shadow.sv
index 8a4f6cf..2af8ea3 100644
--- a/hw/ip/prim/rtl/prim_subreg_shadow.sv
+++ b/hw/ip/prim/rtl/prim_subreg_shadow.sv
@@ -40,8 +40,8 @@
   // W1C is forbidden since the W0S complement is not implemented.
   `ASSERT_INIT(CheckSwAccessIsLegal_A,
       SwAccess inside {SwAccessRW, SwAccessRO, SwAccessWO, SwAccessW1S, SwAccessW0C, SwAccessRC})
-  parameter sw_access_e InvertedSwAccess = (SwAccess == SwAccessW1S) ? SwAccessW0C :
-                                           (SwAccess == SwAccessW0C) ? SwAccessW1S : SwAccess;
+  localparam sw_access_e InvertedSwAccess = (SwAccess == SwAccessW1S) ? SwAccessW0C :
+                                            (SwAccess == SwAccessW0C) ? SwAccessW1S : SwAccess;
 
   // Subreg control signals
   logic          phase_clear;