line_consumption: Fix clint errors

* Fix clint errors that were the results of fixes after adding
  line_consumption.c to the list of files compiled with -Wconversion
line_consumption: Fix conversion error on 32bit machines

* After changing a variable type from int to `int64_t` compilation failed on
  32bit architectures due to a conversion warning. Changing it to `int32_t`
  makes the build fail on 64bit architectures.