[flang] Fixed initialization of c_ptr/c_funptr arrays.

When lowering ends up outlining the initialization of an entity
containing an array of c_ptr/c_funptr it is treating the array
initializer as scalar due to the missing check for the rank.
When initializing non-0 rank c_ptr/c_funptr entity it has to
recurse via genConstantValue().

Reviewed By: clementval

Differential Revision: https://reviews.llvm.org/D150903