v21.06: linux-qcom-sdm845: upgrade to 5.12.15 (backport of MR 2333)
Simple cherry-pick of 07b7a15b from !2333 (merged)
Fixes annoying "random" crashes on the Oneplus 6[T]!
Not sure if I should've removed the MR number and [ci] metadata from the commit message.
CC @calebccff