staging: comedi: Make COMEDI_FC a hidden Kconfig option

staging: comedi: Make COMEDI_FC a hidden Kconfig option

The COMEDI_FC Kconfig option is selected by the relevant drivers
when needed. Since it only contains shared functions, selecting
it manually serves no purpose. Just make it a hidden selection.

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