platform: introduce OF style 'modalias' support for platform bus

Fix a problem that, the platform bus supports the OF style modalias
in .uevent() call, but not in its device 'modalias' sysfs attribute.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index 2f4aea2..bc78848 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -679,6 +679,10 @@
 	struct platform_device	*pdev = to_platform_device(dev);
 	int len;
 
+	len = of_device_get_modalias(dev, buf, PAGE_SIZE -1);
+	if (len != -ENODEV)
+		return len;
+
 	len = acpi_device_modalias(dev, buf, PAGE_SIZE -1);
 	if (len != -ENODEV)
 		return len;