staging: lustre: lnet: add static to libcfs_dev declaration

Add a static prefix to the declaration for libcfs_dev. This would fix
the following sparse warning:

drivers/staging/lustre/lnet/libcfs/module.c:317:19: warning: symbol
'libcfs_dev' was not declared. Should it be static?

Signed-off-by: Justin Skists <justin.skists@juzza.co.uk>
Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>