target-mips: don't use local temps for store conditional

Store conditional operations only need local temps in user mode. Fix
the code to use temp local only in user mode, this spares two memory
stores in system mode.

At the same time remove a wrong a wrong copied & pasted comment,
store operations don't have a register destination.
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

target-mips/translate.c

@@ -1814,13 +1814,14 @@ static void gen_st_cond (DisasContext *ctx, uint32_t opc, int rt,
     const char *opn = "st_cond";
     TCGv t0, t1;
 
+#ifdef CONFIG_USER_ONLY
     t0 = tcg_temp_local_new();
-
-    gen_base_offset_addr(ctx, t0, base, offset);
-    /* Don't do NOP if destination is zero: we must perform the actual
-       memory access. */
-
     t1 = tcg_temp_local_new();
+#else
+    t0 = tcg_temp_new();
+    t1 = tcg_temp_new();
+#endif
+    gen_base_offset_addr(ctx, t0, base, offset);
     gen_load_gpr(t1, rt);
     switch (opc) {
 #if defined(TARGET_MIPS64)