Hi, I confused about why do the key sensor to sweep sensor operation again in the line [116](https://github.com/Megvii-BaseDetection/BEVStereo/blob/62711e779472dac5907b2622b227416e3694e131/layers/backbones/lss_fpn.py#L1116) 
Hi,
I confused about why do the key sensor to sweep sensor operation again in the line 116