irqchip/aslint-sswi: Fix error check of of_io_request_and_map() result

irqchip/aslint-sswi: Fix error check of of_io_request_and_map() result

of_io_request_and_map() returns IOMEM_ERR_PTR() on failure which is
non-NULL.

Fixes: 8a7f030df897 ("irqchip/aslint-sswi: Request IO memory resource")
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Vladimir Kondratiev <vladimir.kondratiev@mobileye.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260118082843.2786630-1-vladimir.kondratiev@mobileye.com
Closes: https://lore.kernel.org/all/20260116124257.78357-1-clm@meta.com