drivers/ptp: Convert snprintf to sysfs_emit

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

coccinelle complains that there are still a couple of functions that use
snprintf(). Convert them to sysfs_emit().

> ./drivers/ptp/ptp_sysfs.c:27:8-16: WARNING: please use sysfs_emit

No functional change intended

Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Link: https://lore.kernel.org/r/20240125015329.123023-1-lizhijian@fujitsu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>