ATA: convert GSI to irq on ia64

If an ATA drive uses legacy mode, ata driver will choose 14 and 15 as the
fixed irq number.  On ia64 platform, such numbers are GSI and should be
converted to irq vector.

Signed-off-by: Zhang Yanmin <yanmin.zhang@intel.com>
Cc: Jeff Garzik <jeff@garzik.org>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>