staging: comedi: Kconfig: COMEDI_NI_AT_A2150 should select COMEDI_FC

commit 34ffb33e09132401872fe79e95c30824ce194d23 upstream.

The 'ni_at_a2150' module links to `cfc_write_to_buffer` in the
'comedi_fc' module, so selecting 'COMEDI_NI_AT_A2150' in the kernel
config needs to also select 'COMEDI_FC'.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>