dma: pl08x: allow zero slave channels

It might happen that a platform wants to use its DMA engine for
memcpy only, and then we have zero slave channels to initialize,
so allow the slave initialization to return zero.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/amba-pl08x.c

@@ -2167,7 +2167,7 @@ static int pl08x_probe(struct amba_device *adev, const struct amba_id *id)
 	/* Register slave channels */
 	ret = pl08x_dma_init_virtual_channels(pl08x, &pl08x->slave,
 			pl08x->pd->num_slave_channels, true);
-	if (ret <= 0) {
+	if (ret < 0) {
 		dev_warn(&pl08x->adev->dev,
 			"%s failed to enumerate slave channels - %d\n",
 				__func__, ret);