amd/vpelib: Fix CodeQL issues Pt1

[WHY]
Redundant / inconsisten nullptr checks

Reviewed-by: Jude Shih <Jude.Shih@amd.com>
Reviewed-by: Evan Damphousse <Evan.Damphousse@amd.com>
Acked-by: ChuanYu Tseng <ChuanYu.Tseng@amd.com>
Signed-off-by: Krunoslav Kovac <Krunoslav.Kovac@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35012>
2 files changed