[MIPS] tlb-r4k: Nuke broken paranoia error test.

Bug originally found and reported by Julia Lawall <julia@diku.dk>.  I
decieded that the whole error check was mostly useless paranoia and should
be discarded.  It would only ever trigger if r3k_have_wired_reg has a wrong
value.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>