drm/panfrost: Shrink sched_lock

drm/scheduler requires a lock between _init and _push_job, but the
reservation lock dance doesn't. So shrink the critical section a
notch.

v2: Lucas pointed out how this should really work, I got it all wrong
in v1.
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Rob Herring <robh@kernel.org>
Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210622165511.3169559-5-daniel.vetter@ffwll.ch

drivers/gpu/drm/panfrost/panfrost_job.c

@@ -224,14 +224,13 @@ int panfrost_job_push(struct panfrost_job *job)
 	struct ww_acquire_ctx acquire_ctx;
 	int ret = 0;
 
-	mutex_lock(&pfdev->sched_lock);
 
 	ret = drm_gem_lock_reservations(job->bos, job->bo_count,
 					    &acquire_ctx);
-	if (ret) {
-		mutex_unlock(&pfdev->sched_lock);
+	if (ret)
 		return ret;
-	}
+
+	mutex_lock(&pfdev->sched_lock);
 
 	ret = drm_sched_job_init(&job->base, entity, NULL);
 	if (ret) {