Store on vec may take pointer to constant type

[steffenlarsen]

The store member function on sycl::vec takes a multi_ptr<DataT, ...> argument without considering whether or not DataT is const. Since the function intends to write to the pointer this seems unintentional. If this is intentional, this function is affected by the same problem as described in #540.

Possible solution: Change the signature to:

template <access::address_space AddressSpace, access::decorated IsDecorated>
void store(size_t offset, multi_ptr<std::remove_const_t<DataT>, AddressSpace, IsDecorated> ptr) const;