of_iomap() doesn't return error pointers, it returns NULL. Fix the error
checking to check for NULL pointers.
Fixes: 86cd4301c285 ("irqchip/aspeed-scu-ic: Refactor driver to support variant-based initialization") Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>