staging: comedi: amplc_pci224: absorb pci224_attach_common()

`pci224_attach_common()` is now only called from `pci225_auto_attach()`,
so absorb it into that function.

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>