py/objcell: Fix printing of cell ID/pointer.

On the nanbox build, `o->obj` is a 64-bit type but `%p` formats a 32-bit
type, leading to undefined behavior.

Print the cell's ID as a hex integer instead.

This location was found using an experimental gcc plugin for `mp_printf`
error checking.

Signed-off-by: Jeff Epler <[email protected]>

Author: jepler

py/objcell.c

@@ -30,7 +30,7 @@
 static void cell_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t kind) {
     (void)kind;
     mp_obj_cell_t *o = MP_OBJ_TO_PTR(o_in);
-    mp_printf(print, "<cell %p ", o->obj);
+    mp_printf(print, "<cell " HEX_FMT " ", (mp_uint_t)o->obj);
     if (o->obj == MP_OBJ_NULL) {
         mp_print_str(print, "(nil)");
     } else {