drm/imagination: Rename fence returned by pvr_queue_job_arm()

drm/imagination: Rename fence returned by pvr_queue_job_arm()

Rename from done_fence to finished_fence, both because the function
returns a drm_sched_fence's finished fence, and to avoid confusion with
the job fence, which is called the same but has a different purpose.

Signed-off-by: Alessio Belle <alessio.belle@imgtec.com>
Reviewed-by: Brajesh Gupta <brajesh.gupta@imgtec.com>
Link: https://patch.msgid.link/20260330-job-submission-fixes-cleanup-v1-5-7de8c09cef8c@imgtec.com
Signed-off-by: Matt Coster <matt.coster@imgtec.com>