rem: s32 CARD_Unmount(u32 chn)
add: s32 CARD_Unmount(s32 chn)
context: s32 CARD_Unmount(u32 chn){	s32 ret;	card_block *card = NULL;	if(chn<EXI_CHANNEL_0 || chn>=EXI_CHANNEL_2) return CARD_ERROR_NOCARD;	if((ret=__card_getcntrlblock(chn,&card))<0) ret = CARD_ERROR_NOCARD;	__card_dounmount(chn,ret);	return CARD_ERROR_READY;}