staging: comedi: ni_labpc_cs: local symbols should not be exported

The symbol labpc_cs_driver and the functions labpc_init_module()
and labpc_exit_module() are only referenced in this file. Make
them static.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>