ast: use more suitable types in a few ast nodes

ast: use more suitable types in a few ast nodes

The int ones cannot be signed (they come as such from the scanner, and
NEGATE is never applied to them).

The uint32_t one is really an atom, but presumably the type was never
converted to xkb_atom_t.

Signed-off-by: Ran Benita <ran234@gmail.com>