x86/shadow: fix big-memory build

Modifiers to the pointer passed into list_next_entry() are also being
applied to the macro's return type, and hence if the input pointer is
const-qualified a variable the result gets assigned to would also need
to be. As that doesn't seem desirable here, drop the const qualifier
on the input pointer instead.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/mm/shadow/private.h
+++ b/xen/arch/x86/mm/shadow/private.h
@@ -607,7 +607,7 @@ static inline void sh_put_ref(struct dom
 /* Walk the list of pinned shadows, from the tail forwards,
  * skipping the non-head-page entries */
 static inline struct page_info *
-prev_pinned_shadow(const struct page_info *page,
+prev_pinned_shadow(struct page_info *page,
                    const struct domain *d)
 {
     struct page_info *p;