uio: fix irq init with dt support & irq not defined

This change also does a bit of a unification for the IRQ init code.

But the actual problem is that UIO_IRQ_NONE == 0, so for the DT case where
UIO_IRQ_NONE gets assigned to `uioinfo->irq`, a 2nd initialization will get
triggered (for the IRQ) and this one will exit via `goto bad1`.

As far as things seem to go, the only case where UIO_IRQ_NONE seems valid,
is when using a device-tree. The driver has some legacy support for old
platform_data structures. It looks like, for platform_data a non-existent
IRQ is an invalid case (or was considered an invalid case).
Which is why -ENXIO is treated only when a DT is used.
Signed-off-by: Dragos Bogdan <dragos.bogdan@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Acked-by: Damian Hobson-Garcia <dhobsong@igel.co.jp>
Link: https://lore.kernel.org/r/20191105073212.16719-1-alexandru.ardelean@analog.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/uio/uio_dmem_genirq.c

@@ -151,8 +151,6 @@ static int uio_dmem_genirq_probe(struct platform_device *pdev)
 	int i;
 
 	if (pdev->dev.of_node) {
-		int irq;
-
 		/* alloc uioinfo for one device */
 		uioinfo = kzalloc(sizeof(*uioinfo), GFP_KERNEL);
 		if (!uioinfo) {
@@ -163,13 +161,6 @@ static int uio_dmem_genirq_probe(struct platform_device *pdev)
 		uioinfo->name = devm_kasprintf(&pdev->dev, GFP_KERNEL, "%pOFn",
 					       pdev->dev.of_node);
 		uioinfo->version = "devicetree";
-
-		/* Multiple IRQs are not supported */
-		irq = platform_get_irq(pdev, 0);
-		if (irq == -ENXIO)
-			uioinfo->irq = UIO_IRQ_NONE;
-		else
-			uioinfo->irq = irq;
 	}
 
 	if (!uioinfo || !uioinfo->name || !uioinfo->version) {
@@ -199,8 +190,11 @@ static int uio_dmem_genirq_probe(struct platform_device *pdev)
 	mutex_init(&priv->alloc_lock);
 
 	if (!uioinfo->irq) {
+		/* Multiple IRQs are not supported */
 		ret = platform_get_irq(pdev, 0);
-		if (ret < 0)
+		if (ret == -ENXIO && pdev->dev.of_node)
+			ret = UIO_IRQ_NONE;
+		else if (ret < 0)
 			goto bad1;
 		uioinfo->irq = ret;
 	}