genirq/chip: Add buslock back in to irq_set_handler()

genirq/chip: Add buslock back in to irq_set_handler()

The locking was changed from a buslock to a plain lock, but the patch
description states there was no functional change. Assuming this was
accidental so reverting to using the buslock.

Fixes: 5cd05f3e2315 ("genirq/chip: Rework irq_set_handler() variants")
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://patch.msgid.link/20251023154901.1333755-2-ckeepax@opensource.cirrus.com