dma_request_chan result check broken

[DanielO]

If dma_request_chan fails (eg if you have a receive only DMA controller but used channel 0 for Rx rather than 1) then the check for NULL will pass but the driver will later cause a page fault dereferencing the result.

The check should be:

        pchannel_p->channel_p = dma_request_chan(&pdev->dev, name);
        if (IS_ERR(pchannel_p->channel_p)) {
                dev_err(pchannel_p->dma_device_p, "DMA channel request error: %d\n", PTR_ERR(pchannel_p->channel_p));
                return ERROR;
        }