testing/device-oneplus-oneplus3t: update dtb name
Update Oneplus 3T dtb name to match with msm8996-mainline kernel change (https://gitlab.com/msm8996-mainline/linux/-/commit/56b6d19fcc50dad3750d93df3a73498f05275489). After the change pmabootstrap install
completes successfully. This is first of several MR-s