MIPS:fix the RT_EXCEPTION_MAX value
MIPS:fix the RT_EXCEPTION_MAX value

from <see mips run> know that cp0_cause's ExcCode have 5 bit filed and
the max exception is 32.

hezlog/rt-thread,armink/rt-thread,armink/rt-thread,geniusgogo/rt-thread,geniusgogo/rt-thread,geniusgogo/rt-thread,hezlog/rt-thread,RT-Thread/rt-thread,nongxiaoming/rt-thread,nongxiaoming/rt-thread,nongxiaoming/rt-thread,RT-Thread/rt-thread,weety/rt-thread,geniusgogo/rt-thread,nongxiaoming/rt-thread,weety/rt-thread,armink/rt-thread,ArdaFu/rt-thread,ArdaFu/rt-thread,hezlog/rt-thread,ArdaFu/rt-thread,RT-Thread/rt-thread,hezlog/rt-thread,hezlog/rt-thread,armink/rt-thread,geniusgogo/rt-thread,geniusgogo/rt-thread,hezlog/rt-thread,RT-Thread/rt-thread,ArdaFu/rt-thread,nongxiaoming/rt-thread,RT-Thread/rt-thread,nongxiaoming/rt-thread,weety/rt-thread,ArdaFu/rt-thread,hezlog/rt-thread,ArdaFu/rt-thread,geniusgogo/rt-thread,weety/rt-thread,armink/rt-thread,weety/rt-thread,weety/rt-thread,RT-Thread/rt-thread,weety/rt-thread,RT-Thread/rt-thread,ArdaFu/rt-thread,nongxiaoming/rt-thread,armink/rt-thread,armink/rt-thread