[tlul,rtl] Remove a term in tlul_adapter_reg's instr_error signal

The instr_error signal is only used in an OR with tl_err. If the
instr_type field is invalid then u_err (a tlul_err instance) will
cause tl_err to be high (because it's equivalent check will fail). So
there's no need to test it explicitly here.

Note that the instr_error signal is still worth having, because it
allows us to spot when someone does a TL transaction whose user bits
claim to be of "instruction type" but where en_ifetch_i is false.

Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>

hw/ip/tlul/rtl/tlul_adapter_reg.sv

@@ -199,10 +199,8 @@ module tlul_adapter_reg
   ////////////////////
 
   // An instruction type transaction is only valid if en_ifetch is enabled
-  // If the instruction type is completely invalid, also considered an instruction error
-  assign instr_error = prim_mubi_pkg::mubi4_test_invalid(tl_i.a_user.instr_type) |
-                       (prim_mubi_pkg::mubi4_test_true_strict(tl_i.a_user.instr_type) &
-                        prim_mubi_pkg::mubi4_test_false_loose(en_ifetch_i));
+  assign instr_error = prim_mubi_pkg::mubi4_test_true_strict(tl_i.a_user.instr_type) &
+                       prim_mubi_pkg::mubi4_test_false_loose(en_ifetch_i);
 
   assign err_internal = addr_align_err | tl_err | instr_error | intg_error;