mips: cavium: Replace DEFINE_SIMPLE_ATTRIBUTE with DEFINE_DEBUGFS_ATTRIBUTE

Fix the following coccicheck warning:
./arch/mips/cavium-octeon/oct_ilm.c:65:0-23: WARNING:
reset_statistics_ops should be defined with DEFINE_DEBUGFS_ATTRIBUTE

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>