Documentation: Coccinelle: fix various typos etc.

Fix various typos etc. in dev-tools/coccinelle.rst:

- punctuation, grammar, wording

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Julia Lawall <julia.lawall@inria.fr>
Link: https://lore.kernel.org/r/def28907-18b9-5b7a-e743-79b0418c946c@infradead.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>