perf, sparc: Fix CONFIG_PERF_EVENTS=y build error

Fix a typo in:

  004417a6: perf, arch: Cleanup perf-pmu init vs lockup-detector

Which caused a build failure on Sparc, reported by Stephen Rothwell.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>