smb3: fix compiler warning in reparse code

utf8s_to_utf16s() specifies pwcs as a wchar_t pointer (whether big endian
or little endian is passed in as an additional parm), so to remove a
distracting compile warning it needs to be cast as (wchar_t *) in
parse_reparse_wsl_symlink() as done by other callers.

Fixes: 06a7adf3 ("cifs: Add support for parsing WSL-style symlinks")
Reviewed-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>