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: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

target-mips/translate.c

diff --git a/target-mips/translate.c b/target-mips/translate.c
index 05d88c4..2484b23 100644
--- a/target-mips/translate.c
+++ b/target-mips/translate.c
@@ -1814,13 +1814,14 @@
     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)