coccinelle/null: solve parse error

This patch solves the parse-error by adding @@ . This is necessary since
Coccinelle version 1.0.0-rc20. Also, the comment is added to use a
recent version of Coccinelle.

Signed-off-by: Himangi Saraogi <himangi774@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Michal Marek <mmarek@suse.cz>