sim: cgen-trace: tweak printf call

GCC warns that we pass a non-string literal as the format string,
so add an explicit "%s" to make it happy.

sim/common/cgen-trace.c

@@ -169,7 +169,7 @@ cgen_trace_insn (SIM_CPU *cpu, const struct cgen_insn *opcode,
   if (CGEN_INSN_VIRTUAL_P (opcode))
     {
       trace_prefix (CPU_STATE (cpu), cpu, NULL_CIA, pc, 0,
-		    NULL, 0, CGEN_INSN_NAME (opcode));
+		    NULL, 0, "%s", CGEN_INSN_NAME (opcode));
       return;
     }