genirq: Use for_each_action_of_desc in actions_show()

Refactor action_show() to use for_each_action_of_desc instead
of a similar open-coded loop.

Signed-off-by: Paran Lee <p4ranlee@gmail.com>
[maz: reword commit message]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220710112614.19410-1-p4ranlee@gmail.com