LoongArch: Fix arch_dup_task_struct() for CONFIG_RANDSTRUCT

LoongArch: Fix arch_dup_task_struct() for CONFIG_RANDSTRUCT

commit a91b446e359aa96cc2655318789fd37441337415 upstream.

Now the optimized version of arch_dup_task_struct() for LoongArch
assumes 'thread' is the last member of 'task_struct'. But this is
not true if CONFIG_RANDSTRUCT is enabled after Linux-6.16.

So fix the arch_dup_task_struct() function for CONFIG_RANDSTRUCT by
copying the whole 'task_struct'.

Cc: stable@vger.kernel.org   # 6.16+
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>