staging: comedi: amplc_pci230: remove some indentation in pci230_ai_check_chanlist()

A few lines in `pci230_ai_check_chanlist()` are indented one level too
much, so remove the excess indentation.

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>