acpi_get_override_irq() followed by acpi_register_gsi() returns negative
error code on failure.

Propagate it from acpi_gsi_to_irq() to callers.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
[ rjw : Subject/changelog ]
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>