LoongArch: Correct the calculation logic of thread_count

LoongArch: Correct the calculation logic of thread_count

For thread_count, the current calculation method has a maximum of 255,
which may not be sufficient in the future. Therefore, we are correcting
it now.

Reference: SMBIOS Specification, 7.5 Processor Information (Type 4)[1]

[1]: https://www.dmtf.org/sites/default/files/standards/documents/DSP0134_3.9.0.pdf

Cc: stable@vger.kernel.org
Signed-off-by: Qiang Ma <maqianga@uniontech.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>