perf/x86/intel/pebs: Fix event disable PEBS buffer drain

perf/x86/intel/pebs: Fix event disable PEBS buffer drain

When disabling a PEBS event, we need to drain the buffer. Doing so
requires a correct cpuc->pebs_active mask.

The current code clears the pebs_active bit before draining the
buffer. Fix that.

Signed-off-by: "Liang, Kan" <kan.liang@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver<vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/37D7C6CF3E00A74B8858931C1DB2F07701885A65@SHSMSX103.ccr.corp.intel.com
[ Fixed the SOB. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>