Fixes non-BFB issue with F-compsets when threading is used

Merge branch 'singhbalwinder/atm/fix-non-BFB-threading-runs' (PR #1219)

This PR addresses an issue which makes the model non-deterministic
(i.e. non-BFB) when run with more than one thread. PR #1147 introduced
a logical variable (cldfsnow_logic) which was declared and assigned at
module level. This kind of declaration automatically sets a variable
with 'SAVE' attribute which in turn makes the variable a shared variable
(to be shared by all the threads). This PR removes this variables and
retain the same functionality.

Fixes #1203

[BFB] - Bit-For-Bit