drm/msm/adreno: Assign msm_gpu->pdev earlier to avoid nullptrs
In the Linux kernel, the following vulnerability has been resolved:

drm/msm/adreno: Assign msm_gpu->pdev earlier to avoid nullptrs

There are some cases, such as the one uncovered by Commit 46d4efcccc68
("drm/msm/a6xx: Avoid a nullptr dereference when speedbin setting fails")
where

msm_gpu_cleanup() : platform_set_drvdata(gpu->pdev, NULL);

is called on gpu->pdev == NULL, as the GPU device has not been fully
initialized yet.

Turns out that there's more than just the aforementioned path that
causes this to happen (e.g. the case when there's speedbin data in the
catalog, but opp-supported-hw is missing in DT).

Assigning msm_gpu->pdev earlier seems like the least painful solution
to this, therefore do so.

Patchwork: https://patchwork.freedesktop.org/patch/602742/