perf/x86: Fix typo in comment

No functional change.

Signed-off-by: Su Yanjun <suyj.fnst@cn.fujitsu.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1565945001-4413-1-git-send-email-suyj.fnst@cn.fujitsu.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>