perf_counter: fix alignment in /proc/interrupts

Trivial fix on columns alignment in /proc/interrupts file.

Signed-off-by: Luis Henriques <henrix@sapo.pt>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20090413192449.GA3920@hades.domain.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>