[flang] Handle dispatch on nopass procedure from array element

When a fir.dispatch is done with a NOPASS type-bound
procedure, the object in fir.dispatch is just used to gather the vtable.
Therefore, no transformation is done on it and the original entity
is used. The current code generation didn't expect the entity to be an array.
This patch update the code generation to be able to retrieve the vtable
accordingly.

Reviewed By: PeteSteinfeld

Differential Revision: https://reviews.llvm.org/D137255