kernel/reboot: replace sprintf() with sysfs_emit()

kernel/reboot: replace sprintf() with sysfs_emit()

As Documentation/filesystems/sysfs.rst suggested, show() should only use
sysfs_emit() or sysfs_emit_at() when formatting the value to be returned
to user space.

No functional change intended.

Link: https://lkml.kernel.org/r/20241105094941.33739-1-zhangguopeng@kylinos.cn
Signed-off-by: zhangguopeng <zhangguopeng@kylinos.cn>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>