drm/msm/adreno: adreno_gpu: Switch to memdup_user_nul() helper

Use memdup_user_nul() helper instead of open-coding to simplify the code.

Signed-off-by: Ruan Jinjie <ruanjinjie@huawei.com>
Reviewed-by: Bjorn Andersson <quic_bjorande@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/552130/


Signed-off-by: Rob Clark <robdclark@chromium.org>