drivers: fwnode: fix fwnode_irq_get[_byname]()

The fwnode_irq_get() and the fwnode_irq_get_byname() return 0 upon
device-tree IRQ mapping failure. This is contradicting the
fwnode_irq_get_byname() function documentation and can potentially be a
source of errors like:

int probe(...) {
	...

	irq = fwnode_irq_get_byname();
	if (irq <= 0)
		return irq;

	...
}

Here we do correctly check the return value from fwnode_irq_get_byname()
but the driver probe will now return success. (There was already one
such user in-tree).

Change the fwnode_irq_get_byname() to work as documented and make also the
fwnode_irq_get() follow same common convention returning a negative errno
upon failure.

Fixes: ca0acb5 ("device property: Add fwnode_irq_get_byname")
Suggested-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Message-ID: <3e64fe592dc99e27ef9a0b247fc49fa26b6b8a58.1685340157.git.mazziesaccount@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: M-Vaittinen

drivers/base/property.c

@@ -987,12 +987,18 @@ EXPORT_SYMBOL(fwnode_iomap);
  * @fwnode:	Pointer to the firmware node
  * @index:	Zero-based index of the IRQ
  *
- * Return: Linux IRQ number on success. Other values are determined
- * according to acpi_irq_get() or of_irq_get() operation.
+ * Return: Linux IRQ number on success. Negative errno on failure.
  */
 int fwnode_irq_get(const struct fwnode_handle *fwnode, unsigned int index)
 {
-	return fwnode_call_int_op(fwnode, irq_get, index);
+	int ret;
+
+	ret = fwnode_call_int_op(fwnode, irq_get, index);
+	/* We treat mapping errors as invalid case */
+	if (ret == 0)
+		return -EINVAL;
+
+	return ret;
 }
 EXPORT_SYMBOL(fwnode_irq_get);