drm/v3d: Disable preemption while updating GPU stats

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

drm/v3d: Disable preemption while updating GPU stats

We forgot to disable preemption around the write_seqcount_begin/end() pair

while updating GPU stats:

[ ] WARNING: CPU: 2 PID: 12 at include/linux/seqlock.h:221 __seqprop_assert.isra.0+0x128/0x150 [v3d]

[ ] Workqueue: v3d_bin drm_sched_run_job_work [gpu_sched]

<...snip...>

[ ] Call trace:

[ ] __seqprop_assert.isra.0+0x128/0x150 [v3d]

[ ] v3d_job_start_stats.isra.0+0x90/0x218 [v3d]

[ ] v3d_bin_job_run+0x23c/0x388 [v3d]

[ ] drm_sched_run_job_work+0x520/0x6d0 [gpu_sched]

[ ] process_one_work+0x62c/0xb48

[ ] worker_thread+0x468/0x5b0

[ ] kthread+0x1c4/0x1e0

[ ] ret_from_fork+0x10/0x20

Fix it.