perf/core: Use sysfs_emit() instead of scnprintf()

Follow the advice in Documentation/filesystems/sysfs.rst:

  "- show() should only use sysfs_emit() or sysfs_emit_at() when formatting
     the value to be returned to user space."

No change in functionality intended.

[ mingo: Updated the changelog ]

Signed-off-by: XieLudan <xie.ludan@zte.com.cn>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250315141738452lXIH39UJAXlCmcATCzcBv@zte.com.cn