workqueue: replace BUG_ON with panic in panic_on_wq_watchdog

workqueue: replace BUG_ON with panic in panic_on_wq_watchdog

Replace BUG_ON() with panic() in panic_on_wq_watchdog(). This is not
a bug condition but a deliberate forced panic requested by the user
via module parameters to crash the system for debugging purposes.

Using panic() instead of BUG_ON() makes this intent clearer and provides
more informative output about which threshold was exceeded and the actual
values, making it easier to diagnose the stall condition from crash dumps.

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Tejun Heo <tj@kernel.org>