[IA64] another place to use for_each_cpu_mask() in arch/ia64

In arch/ia64 change the explicit use of a for-loop using NR_CPUS into the
general for_each_online_cpu() construct.  This widens the scope of potential
future optimizations of the general constructs, as well as takes advantage
of the existing optimizations of first_cpu() and next_cpu(), which is
advantageous when the true CPU count is much smaller than NR_CPUS.

Signed-off-by: John Hawkes <hawkes@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>