[memutil] Fix width mismatch

The nonce isn't an int variable, assign a arbitrary-width zero instead
of an "int zero".

Signed-off-by: Philipp Wagner <[email protected]>

hw/ip/prim/rtl/prim_util_get_scramble_params.svh

@@ -29,7 +29,7 @@
       return 0;
     end
 
-    nonce = 0;
+    nonce = '0;
     nonce[NonceWidth-1:0] = nonce_i;
     return 1;
   endfunction