staging: comedi: amplc_pci230: absorb pci230_alloc_private()

`pci230_alloc_private()` is now only called from `pci230_auto_attach()`
to allocate private device storage and initialize various spin-lock
members therein.  Absorb the body of `pci230_alloc_private()` into
`pci230_auto_attach()` itself.

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>