[flang] Fix rank and byte stride in pointer remapping

In some remapping case the rank of the pointer is different
from the target one.

```
program remap
  type :: p
    integer :: a
  end type t
  type(p), target :: ta(10) = [ (t(i),i=1,10) ]
  class(t), pointer :: p(:,:)
  p(1:2,1:5) => ta
end
```

This patch updates the rank and the byte stride to fix such case.

Reviewed By: klausler

Differential Revision: https://reviews.llvm.org/D143566