[ACPI] iosapic_register_intr() now returns error instead of panic

error condition is passed along by acpi_register_gsi().

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>