HID: winwing: Add NULL check in winwing_init_led()

In the Linux kernel, the following vulnerability has been resolved: HID: winwing: Add NULL check in winwing_init_led() devm_kasprintf() can return a NULL pointer on failure,but this returned value in winwing_init_led() is not checked. Add NULL check in winwing_init_led(), to handle kernel NULL pointer dereference error.