mcb: use sysfs_emit_at() instead of scnprintf() in show functions

mcb: use sysfs_emit_at() instead of scnprintf() in show functions

This change improves clarity and ensures proper bounds checking in
line with the preferred sysfs_emit() API usage for sysfs 'show'
functions. The PAGE_SIZE check is now handled internally by the helper.

No functional change intended.

Signed-off-by: Abhinav Ananthu <abhinav.ogl@gmail.com>
Signed-off-by: Johannes Thumshirn <jth@kernel.org>
Reviewed-by: Johannes Thumshirn <jth@kernel.org>
Link: https://lore.kernel.org/r/20250707074720.40051-2-jth@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>