rv: Fix missing mutex unlock in rv_register_monitor()

If create_monitor_dir() fails, the function returns directly without
releasing rv_interface_lock. This leaves the mutex locked and causes
subsequent monitor registration attempts to deadlock.

Fix it by making the error path jump to out_unlock, ensuring that the
mutex is always released before returning.

Fixes: 24cbfe1 ("rv: Merge struct rv_monitor_def into struct rv_monitor")
Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
Reviewed-by: Gabriele Monaco <gmonaco@redhat.com>
Reviewed-by: Nam Cao <namcao@linutronix.de>
Link: https://lore.kernel.org/r/20250903065112.1878330-1-zhen.ni@easystack.cn
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>

Author: nizhen-t

kernel/trace/rv/rv.c

@@ -805,7 +805,7 @@ int rv_register_monitor(struct rv_monitor *monitor, struct rv_monitor *parent)
 
 	retval = create_monitor_dir(monitor, parent);
 	if (retval)
-		return retval;
+		goto out_unlock;
 
 	/* keep children close to the parent for easier visualisation */
 	if (parent)