tools/power turbostat: Fix column printing for PMT xtal_time counters

If the very first printed column was for a PMT counter of type xtal_time
we would misalign the column header, because we were always printing the
delimiter.

Signed-off-by: Patryk Wlazlyn <patryk.wlazlyn@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>