[IA64] simplify some condition checks in iosapic_check_gsi_range

Some condition checks on iosapic_check_gsi_range() can be omitted
because always `base <= end' is assured. This patch simplifies those
checks.

Signed-off-by: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>