Fix recursive loop in parsing pointer to self struct

Fix recursive loop in parsing pointer to self struct

Issue occurs in the description visitor class, when the struct used in a
map key is a pointer to self, as in:

struct node;
struct node {
  struct node *next;
};

Avoid this in the desc by using "unsigned long long" for all pointers.

Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>