spi: rockchip: check requesting dma channel with EPROBE_DEFER

[Dan Carpenter]

Hello Shawn Lin,

The patch 61cadcf46cfd: "spi: rockchip: check requesting dma channel
with EPROBE_DEFER" from Mar 9, 2016, leads to the following static
checker warning:

	drivers/spi/spi-rockchip.c:742 rockchip_spi_probe()
	warn: passing zero to 'PTR_ERR'

drivers/spi/spi-rockchip.c
   732  
   733          rs->dma_tx.ch = dma_request_slave_channel(rs->dev, "tx");
   734          if (IS_ERR_OR_NULL(rs->dma_tx.ch)) {
   735                  /* Check tx to see if we need defer probing driver */
   736                  if (PTR_ERR(rs->dma_tx.ch) == -EPROBE_DEFER) {
   737                          ret = -EPROBE_DEFER;
   738                          goto err_get_fifo_len;

What's going on here?  Are we planning to change dma_request_slave_channel()
to return error pointers?  Also what about other error pointers besides
EPROBE_DEFER it seems dangerous to leave rs->dma_tx.ch as an error
pointer.  We probably eventually try to free it if it's non-NULL.

   739                  }
   740                  dev_warn(rs->dev, "Failed to request TX DMA channel\n");
   741          }
   742  

regards,
dan carpenter