scripts: coccicheck: Use /usr/bin/env

If bash is not located under /bin, coccicheck fails to run.  In the real
world, this happens for instance when NixOS is used in the host.  Instead,
use /usr/bin/env to locate the executable binary for bash.

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Tested-by: Deepak R Varma <drv@mailo.com>
Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>