platform/x86: silicom-platform: Add missing "Description:" for power_cycle sysfs attr

The Documentation/ABI/testing/sysfs-platform-silicom entry
for the power_cycle sysfs attr is missing the "Description:" keyword,
add this.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20240108140655.547261-1-hdegoede@redhat.com