i try to flash my bios from my tablet onda v919 

i try to backup my current bios with this command: sudo flashrom -p ch341a_spi --read backup.bin and i get this error 

Calibrating delay loop... OK. 

Couldn't open device 1a86:5512.

Error: Programmer initialization failed. 

what am i doing wrong? i find this guide to help me https://peejseej.nl/2016/05/flash-an-bricked-onda-v919-air-ch-bios/comment-page-1/