soc: nxp: mcxw: Update IRQ Size for MCXW to remove reserved IRQ

The FRDM_MCXW71 Platform has a reserved IRQ as its
last IRQ, this test was using this IRQ to
test an interrupt and would not fire. This change
ensures the test does not use the reserved IRQ.

Signed-off-by: Emilio Benavente <emilio.benavente@nxp.com>