gpio: omap: Move PM device over to irq domain

Move the reference to the device over to the irq domain.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Tested-by: Tony Lindgren <tony@atomide.com>
Acked-by: Bartosz Golaszewski <brgl@bgdev.pl>
Link: https://lore.kernel.org/r/20220201120310.878267-8-maz@kernel.org