genirq/msi: Use lock guards for MSI descriptor locking

Provide a lock guard for MSI descriptor locking and update the core code
accordingly.

No functional change intended.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/all/20250319105506.144672678@linutronix.de