irqchip/mbigen: Fix return value check in mbigen_device_probe()

In case of error, the function devm_ioremap() returns NULL pointer
not ERR_PTR(). Use devm_ioremap_resource() instead of devm_ioremap()
to fix the IS_ERR() test issue.

Fixes: 76e1f77f

 ("irqchip/mbigen: Introduce mbigen_of_create_domain()")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Link: http://lkml.kernel.org/r/20170427152113.31147-1-weiyj.lk@gmail.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>