arm-ccn: use platform_get_irq to get IRQ

Since a1a2b712 ("of/platform: Drop static setup of IRQ resource
from DT core"), the static setup of IRQ resource was dropped, all
the DT drivers have switched to platform_get_irq(), adjust arm-ccn
driver accordingly.

Signed-off-by: Liwei Song <liwei.song@windriver.com>