dma: of: Remove restriction that #dma-cells can't be 0

There is no sensible reason why #dma-cells shouldn't be allowed to be 0. It is
completely up to the DMA controller how many additional parameters, besides the
phandle, it needs to identify a channel. E.g. for DMA controller with only one
channel or for DMA controllers which don't have a restriction on which channel
can be used for which peripheral it completely legitimate to not require any
additional parameters.

Also fixes the following warning:
drivers/dma/of-dma.c: In function 'of_dma_controller_register':
drivers/dma/of-dma.c:67:7: warning: 'nbcells' may be used uninitialized in this function

Signed-off-by: Lars-Peter Clausen <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Vinod Koul <[e-mail]>

drivers/dma/of-dma.c

···
 				void *data)
 {
 	struct of_dma	*ofdma;
-	int		nbcells;
 	const __be32	*prop;
 
 	if (!np || !of_dma_xlate) {
···
 		return -ENOMEM;
 
 	prop = of_get_property(np, "#dma-cells", NULL);
-	if (prop)
-		nbcells = be32_to_cpup(prop);
-
-	if (!prop || !nbcells) {
-		pr_err("%s: #dma-cells property is missing or invalid\n",
+	if (!prop) {
+		pr_err("%s: #dma-cells property is missing\n",
 		       __func__);
 		kfree(ofdma);
 		return -EINVAL;
 	}
 
+
 	ofdma->of_node = np;
-	ofdma->of_dma_nbcells = nbcells;
+	ofdma->of_dma_nbcells = be32_to_cpup(prop);
 	ofdma->of_dma_xlate = of_dma_xlate;
 	ofdma->of_dma_data = data;