sensors-detect: Use modules.builtin instead of /sys/module

/sys/module doesn't actually contain all built-in modules, only the
ones which have a version or at least one parameter. Better use file
modules.builtin which is generated since kernel 2.6.33, it is complete
and this will let us handle built-in modules properly.
sensors-detect: Handle built-in modules properly

We now have everything we need to handle built-in modules properly, so
do it. It should work fine since kernel 2.6.33.