linux-user/loongarch64: setup_sigframe() set 'end' context size 0

See:
  https://github.com/torvalds/linux/blob/master/arch/loongarch/kernel/signal.c



The kernel setup_sigcontext() set end context size 0.

Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20231101030816.2353416-4-gaosong@loongson.cn>

linux-user/loongarch64/signal.c

@@ -154,7 +154,7 @@ static void setup_sigframe(CPULoongArchState *env,
      */
     info = extctx->end.haddr;
     __put_user(0, &info->magic);
-    __put_user(extctx->end.size, &info->size);
+    __put_user(0, &info->size);
 }
 
 static bool parse_extcontext(struct extctx_layout *extctx, abi_ptr frame)