Fix compile warnings

Fix 4 compile warnings.

````
$ make
==> erlsom (compile)
Compiled src/erlsom_add.erl
Compiled src/erlsom.erl
src/erlsom_compile.erl:369: Warning: variable 'EfdParent' is unused
src/erlsom_compile.erl:370: Warning: variable 'AfdParent' is unused
src/erlsom_compile.erl:779: Warning: variable 'Max' is unused
src/erlsom_compile.erl:779: Warning: variable 'Min' is unused
Compiled src/erlsom_compile.erl
````