Only the ISA versions of the LabPC boards support DMA and the
devpriv->dma_chan is only set during the ISA board attach if
DMA is available. The extra check of the board->bustype is not
necessary in labpc_ai_cmd().
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com> Reviewed-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>