x86/ioapic: Return suitable error code in mp_map_gsi_to_irq()

mp_map_gsi_to_irq() in some cases might return legacy -1, which would be
wrongly interpreted as -EPERM.

Correct those cases to return proper error code.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: http://lkml.kernel.org/r/20170119192425.189899-2-andriy.shevchenko@linux.intel.com


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