static_call: Replace pointless WARN_ON() in static_call_module_notify()

In the Linux kernel, the following vulnerability has been resolved: static_call: Replace pointless WARN_ON() in static_call_module_notify() static_call_module_notify() triggers a WARN_ON(), when memory allocation fails in __static_call_add_module(). That's not really justified, because the failure case must be correctly handled by the well known call chain and the error code is passed through to the initiating userspace application. A memory allocation fail is not a fatal problem, but the WARN_ON() takes the machine out when panic_on_warn is set. Replace it with a pr_warn().