staging: comedi: comedi_fc: remove unnecessary prefix in dev_warn() message

The dev_warn() will automatically have the "comedi" prefix.

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