Fix duplicate flag check in constr_CHOICE.c
When using this library in OAI with a linter, a warning was raised in constr_CHOICE.c that there is a duplicate check in an if statement here: if((elm1->flags & ATF_POINTER) && (elm1->flags & ATF_POINTER)){
. This revision changes the check to correctly check elm2
flags instead of doing 2 checks on elm1. This was likely just a copy-paste error.