coccinelle: returnvar: Use imperative mood

coccinelle: returnvar: Use imperative mood

According to Documentation/SubmittingPatches:

"Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
to do frotz", as if you are giving orders to the codebase to change
its behaviour."

So do as recommended.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Michal Marek <mmarek@suse.cz>