[bsp/raspi3-32] fix some bug of funtion '__rt_ffs' (#6187)
[bsp/raspi3-32] fix some bug of funtion '__rt_ffs' (#6187)

* [bsp/raspi3-32] fix some bug of funtion '__rt_ffs'

* Update trap.c

Co-authored-by: Man, Jianting (Meco) <0fc0d424b3d1e2f837d33f3ac71f4dcb4750771e@qq.com>
RT-Thread/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread