staging: comedi: comedi_fc: use comedi_bytes_per_scan()

Since `cfc_bytes_per_scan()` is just an inline function that calls
`comedi_bytes_per_scan()`, replace calls to the former to the latter in
the "comedi_fc" module.  This is part of the migration of functionality
from the "comedi_fc" module to the core "comedi" module.

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