Staging: lustre: obdclass: Declare cl_env_peek as static

Declare cl_env_peek as static since it is used only in this file.
Also remove the EXPORT SYMBOL.

Signed-off-by: Shraddha Barke <shraddha.6596@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>