stop_machine: Remove this_cpu_ptr() from print_stop_info().

This aligns the patch ("stop_machine: Add function and caller debug
info) with commit
  a8b62fd085050 ("stop_machine: Add function and caller debug info")

that was merged upstream and is slightly different.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>