firmware: meson_sm: fix device leak at probe

Make sure to drop the reference to the secure monitor device taken by
of_find_device_by_node() when looking up its driver data on behalf of
other drivers (e.g. during probe).

Note that holding a reference to the platform device does not prevent
its driver data from going away so there is no point in keeping the
reference after the helper returns.

Fixes: 8cde3c2153e8 ("firmware: meson_sm: Rework driver as a proper platform driver")
Cc: [e-mail] # 5.5
Cc: Carlo Caione <[e-mail]>
Signed-off-by: Johan Hovold <[e-mail]>
Acked-by: Martin Blumenstingl <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Neil Armstrong <[e-mail]>

drivers/firmware/meson/meson_sm.c

···
 struct meson_sm_firmware *meson_sm_get(struct device_node *sm_node)
 {
 	struct platform_device *pdev = of_find_device_by_node(sm_node);
+	struct meson_sm_firmware *fw;
 
 	if (!pdev)
 		return NULL;
 
-	return platform_get_drvdata(pdev);
+	fw = platform_get_drvdata(pdev);
+
+	put_device(&pdev->dev);
+
+	return fw;
 }
 EXPORT_SYMBOL_GPL(meson_sm_get);