perf_counter: fix print debug irq disable

inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage.
bash/15802 [HC0[0]:SC0[0]:HE1:SE1] takes:
 (sysrq_key_table_lock){?.....},

Don't unconditionally enable interrupts in the perf_counter_print_debug()
path.

[ Impact: fix potential deadlock pointed out by lockdep ]

LKML-Reference: <new-submission>
Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>