perf/x86/intel: Fix sparse warning

Signed-off-by: Yan, Zheng <[e-mail]>
Signed-off-by: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/kernel/cpu/perf_event_intel_uncore.c

···
 	if (!uncore_box_is_fake(box))
 		reg1->alloc |= alloc;
 
-	return 0;
+	return NULL;
 fail:
 	for (; i >= 0; i--) {
 		if (alloc & (0x1 << i))