[IA64] Remove vector from ia64_machine_kexec()

The use of vector in ia64_machine_kexec() seems spurious,
and removing it simplifies the code slightly.

As suggested by Alex Williamson <alex.williamson@hp.com>

Cc: Alex Williamson <alex.williamson@hp.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Tony Luck <tony.luck@intel.com>