As mentioned by Rohan KODA, 賀茂 and 慶滋 are synonymous with each other, but of different characters, and considering that Yasutane's brothers were identifying themselves as 慶滋, the original pronunciation would probably be 'kamo.'
露伴の言うように、賀茂と慶滋は異字同義であり、保胤の弟らも同じく慶滋を名乗っていることから、恐らく本来のよみは「かも」であろう。