powerpc/8xx: Fix interrupt mask in cpm1_gpiochip_add16()

powerpc/8xx: Fix interrupt mask in cpm1_gpiochip_add16()

Allthough fsl,cpm1-gpio-irq-mask always contains a 16 bits value,
it is a standard u32 OF property as documented in
Documentation/devicetree/bindings/soc/fsl/cpm_qe/gpio.txt

The driver erroneously uses of_property_read_u16() leading to a
mask which is always 0.

Fix it by using of_property_read_u32() instead.

Fixes: 726bd223105c ("powerpc/8xx: Adding support of IRQ in MPC8xx GPIO")
Signed-off-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/bb0b6d6c4543238c38d5d29a776d0674a8c0c180.1776752750.git.chleroy@kernel.org