target/loongarch: fix bad shift in check_ps()

In expression 1ULL << tlb_ps, left shifting by more than 63 bits has
undefined behavior. The shift amount, tlb_ps, is as much as 64. check
"tlb_ps >=64" to fix.

Resolves: Coverity CID 1593475

Fixes: d882c284a3 ("target/loongarch: check tlb_ps")
Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Bibo Mao <maobibo@loongson.cn>