macintosh/ams: Replace snprintf in show functions with sysfs_emit

show() must not use snprintf() when formatting the value to be returned
to user space.

Fix the following coccicheck warning:
  drivers/macintosh/ams/ams-core.c:53: WARNING: use scnprintf or sprintf.

Use sysfs_emit instead of scnprintf or sprintf makes more sense.

Signed-off-by: Qing Wang <wangqing@vivo.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1634280544-4581-1-git-send-email-wangqing@vivo.com