coccicheck: return proper error code on fail

If coccicheck fails, it should return an error code distinct from zero
to signal about an internal problem. Current code instead of exiting with
the tool's error code returns the error code of 'echo "coccicheck failed"'
which is almost always equals to zero, thus failing the original intention
of alerting about a problem. This patch fixes the code.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Denis Efremov <efremov@linux.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>