x86, intr-remapping: fix free_irte() to clear all the IRTE entries

Impact: fix interrupt table entry leak

Fix the typo which was not clearing all the interrupt remapping table
entries corresponding to an irq.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>