Function sys_dlist_peek_head_not_empty

pub unsafe extern "C" fn sys_dlist_peek_head_not_empty(
    list: *mut _dnode,
) -> *mut _dnode

@brief get a reference to the head item in the list

The list must be known to be non-empty.

@param list the doubly-linked list to operate on

@return a pointer to the head element