MIPS: IP32: Fix needlessly global symbols in arch/mips/sgi-ip32/ip32-irq.c

The following symbols are needlessly defined global: cpuerr_irq and
memerr_irq. This patch makes the symbols static.

Signed-off-by: Dmitri Vorobiev <dmitri.vorobiev@movial.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>