LSM: fix documentation for sb_copy_data hook

The @type argument of the sb_copy_data hook was removed
in the commit "LSM/SELinux: Interfaces to allow FS to control
mount options" (e0007529). This commit removes the description
of the @type argument from the LSM documentation.

Signed-off-by: Denis Efremov <efremov@ispras.ru>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: James Morris <james.morris@microsoft.com>