perf/x86/intel: Fix sparse warning

Signed-off-by: NYan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1370421025-10986-1-git-send-email-zheng.z.yan@intel.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

arch/x86/kernel/cpu/perf_event_intel_uncore.c

@@ -536,7 +536,7 @@ __snbep_cbox_get_constraint(struct intel_uncore_box *box, struct perf_event *eve
 	if (!uncore_box_is_fake(box))
 		reg1->alloc |= alloc;
 
-	return 0;
+	return NULL;
 fail:
 	for (; i >= 0; i--) {
 		if (alloc & (0x1 << i))