sensordevice: Dummy ALS: Solve fortified libc warning

convert sprint to snprintf, the size of the writes is always known

Change-Id: I53ee36b67544ac25de7e5c05ce90b6817c8a9c92
Merge pull request #1 from CyanogenMod/cm-10.1

sensordevice: Dummy ALS: Solve fortified libc warning