CVE-2024-44993: drm/v3d: Fix out-of-bounds read in `v3d_csd_job_run()`

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

drm/v3d: Fix out-of-bounds read in v3dcsdjobrun()

When enabling UBSAN on Raspberry Pi 5, we get the following warning:

[ 387.894977] UBSAN: array-index-out-of-bounds in drivers/gpu/drm/v3d/v3dsched.c:320:3 [ 387.903868] index 7 is out of range for type 'u32 [7]' [ 387.909692] CPU: 0 PID: 1207 Comm: kworker/u16:2 Tainted: G WC 6.10.3-v8-16k-numa #151 [ 387.919166] Hardware name: Raspberry Pi 5 Model B Rev 1.0 (DT) [ 387.925961] Workqueue: v3dcsd drmschedrunjobwork [gpusched] [ 387.932525] Call trace: [ 387.935296] dumpbacktrace+0x170/0x1b8 [ 387.939403] showstack+0x20/0x38 [ 387.942907] dumpstacklvl+0x90/0xd0 [ 387.946785] dumpstack+0x18/0x28 [ 387.950301] ubsanhandleoutofbounds+0x98/0xd0 [ 387.955383] v3dcsdjobrun+0x3a8/0x438 [v3d] [ 387.960707] drmschedrunjobwork+0x520/0x6d0 [gpusched] [ 387.966862] processonework+0x62c/0xb48 [ 387.971296] workerthread+0x468/0x5b0 [ 387.975317] kthread+0x1c4/0x1e0 [ 387.978818] retfromfork+0x10/0x20 [ 387.983014] ---[ end trace ]---

This happens because the UAPI provides only seven configuration registers and we are reading the eighth position of this u32 array.

Therefore, fix the out-of-bounds read in v3dcsdjobrun() by accessing only seven positions on the 'u32 [7]' array. The eighth register exists indeed on V3D 7.1, but it isn't currently used. That being so, let's guarantee that it remains unused and add a note that it could be set in a future patch.