scripts: coccicheck: fix troubles on non-English builds

When LANG is not set to English, the logic which checks the
number of CPUs fail, as the messages can be localized, and
the logic at:

    THREADS_PER_CORE=$(lscpu | grep "Thread(s) per core: " | tr -cd "[:digit:]")

will not get the number of threads per core.

This causes the script to not run properly, as it will produce
a warning:

	$ make coccicheck COCCI=$PWD/scripts/coccinelle/misc/add_namespace.cocci MODE=report drivers/media/
	./scripts/coccicheck: linha 93: [: número excessivo de argumentos

Fix it by forcing LANG=C when calling lscpu.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>