minor fix for tlb manipulations

[Naoki Hamada]

Hello,

I now realized that I was wrong, and why I was wrong. I have got the
idea of  the fix when I was tracing the execution of FreeBSD/mips on
an AMD5120 system emulated by virtualmips (on Linux!). Its CONFIG1
register shows that there are 32 tlb 'entries', but actually a genuine
ADM5120 tells that there are only 16 'entries'. I hastily assumed that
this emulator worked correctly, and got wrong conclusion. I will
report virtualmips guys this story.

Moral: be careful about emulators. They are merely feeble softwares.

Naoki Hamada
nao at tom-yam.or.jp