Receive &Ptr instead of Ptr in PtrValueIter::new

[lucic71]

let start: Value<Ptr<u8>> = ...;
PtrValueIter::new((*start.borrow()), __count).collect::<Vec<_>>()

tries to move out of (*start.borrow()) which does not implement the Copy trait because Ptr does not implement Copy.

To avoid the move, change the ptr argument of PtrValueIter::new to &Ptr<T> instead of Ptr<T>

pub fn new(ptr: &Ptr<T>, n: usize) -> Self 
                ^

This pattern is not new, it's also used in Ptr::memcpy, Ptr::memset, Ptr::slice_until.