armv7-m/arch_nvic:: Fix typecasting

Created by: nicola-mazzucato-arm

The type of "irq" needs to be aligned with IRQn_Type.

This patch fixes that.

Change-Id: I8fb5a4d9d891e78f01d6088aaad27d9c69daa9ef Signed-off-by: Nicola Mazzucato nicola.mazzucato@arm.com