drm/panthor: Check debugfs GEM lock initialization

drmm_mutex_init() can fail while registering the managed cleanup action.
When that happens, drmm_add_action_or_reset() destroys the mutex before
returning the error. Continuing initialization would therefore leave the
debugfs GEM object list with an unusable lock.

Propagate the error as is already done for the other managed mutexes in
panthor_device_init().

Fixes: a3707f5 ("drm/panthor: show device-wide list of DRM GEM objects over DebugFS")
Signed-off-by: Linmao Li <lilinmao@kylinos.cn>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patch.msgid.link/20260713082912.321021-1-lilinmao@kylinos.cn
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>

Author: Linmao Li

drivers/gpu/drm/panthor/panthor_device.c

@@ -182,7 +182,10 @@ int panthor_device_init(struct panthor_device *ptdev)
 		return ret;
 
 #ifdef CONFIG_DEBUG_FS
-	drmm_mutex_init(&ptdev->base, &ptdev->gems.lock);
+	ret = drmm_mutex_init(&ptdev->base, &ptdev->gems.lock);
+	if (ret)
+		return ret;
+
 	INIT_LIST_HEAD(&ptdev->gems.node);
 #endif