irqchip/irq-bcm7038-l1: Use irq_get_irq_data()

Using irq_desc_get_irq_data(irq_to_desc()) to retrieve the irq_data
structure from a virtual interrupt number is going to be problematic to
make irq-bcm7038-l1 a module because irq_to_desc() is not exported, and
there is no intent to export it to modules, see 64a1b95b ("genirq:
Restrict export of irq_to_desc()").

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211020184859.2705451-4-f.fainelli@gmail.com