[IA64] Fix example error injection program

Progam accessed using /sys/devices/system/node/node0/cpu%d/err_inject/
This path only exists for CONFIG_NUMA=y systems.  Better to use
/sys/devices/system/cpu/cpu%d/err_inject/ which is available on all
systems.

Signed-off-by: Tony Luck <tony.luck@intel.com>