[flang] Fix bogus error on recursive ENTRY

An incorrect "Implicit declaration of function '...' has a different result type
than in previous declaration" is being emitted for ENTRY names used
recursively.  The predicate used to check for recursive use only allowed
for scopes of functions, not ENTRYs.

Fixes llvm-test-suite/Fortran/gfortran/regression/whole_file_9.f90.

Differential Revision: https://reviews.llvm.org/D157337