drm/msm/a6xx: Avoid a nullptr dereference when speedbin setting fails

In the Linux kernel, the following vulnerability has been resolved:

drm/msm/a6xx: Avoid a nullptr dereference when speedbin setting fails

Calling a6xx_destroy() before adreno_gpu_init() leads to a null pointer

dereference on:

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

as gpu->pdev is only assigned in:

a6xx_gpu_init()

|_ adreno_gpu_init

|_ msm_gpu_init()

Instead of relying on handwavy null checks down the cleanup chain,

explicitly de-allocate the LLC data and free a6xx_gpu instead.

Patchwork: https://patchwork.freedesktop.org/patch/588919/