staging: lustre: lustre: libcfs: define symbols as static

This patch fixes the following warning using sparse
- warning: symbol 'libcfs_debug_mb' was not declared. Should it be
  static?
- warning: symbol 'portal_enter_debugger' was not declared. Should
  it be static?

Signed-off-by: Chen Weixiang <weixiangx.chen@outlook.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>