Don't copy SB1 cache error handler to uncached memory.

    
This may have made sense on a paranoid day with pass 1 BCM1250 processors
that were throwing cache error exception left and right for no good
reason.  On modern silicion that hardly makes sense and the code had
gotten just an obscurity ...
    
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>