irqchip/gic-v3: Fix irq_complete_ack() comment

When the GIC is in EOImode == 1 in irq_complete_ack() it executes a
priority drop not a deactivation.

Fix the function comment to clarify the behaviour.

Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20241202112518.51178-1-lpieralisi@kernel.org