SYCL: Use get_multi_ptr instead of deprecated get_pointer in wkv6

[qnixsynapse]

According to the SYCL reference, the member function get_pointer of the sycl::local_accessor class has been deprecated in SYCL 2020. This is a one line patch to use get_multi_ptr instead to remove the warning.

[NeoZhangJianyu]

It's good to update the code!

I have a small comment:
Is it possible to keep the original code format (multiple lines)? So that it's easy to know the changed code, like

shared_mem_acc.get_pointer()
to
(float*)shared_mem_acc.get_multi_ptr<sycl::access::decorated::no>().get()

[qnixsynapse]

@NeoZhangJianyu Yes sure. It's my editor's "autoformatter" that does it whenever I edit code. I updated the change.