LoongArch: Fix the write_fcsr() macro

The "write_fcsr()" macro uses wrong the positions for val and dest in
asm. Fix it!

Reported-by: Miao HAO <haomiao19@mails.ucas.ac.cn>
Signed-off-by: Qi Hu <huqi@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>