of/device: Replace struct of_device with struct platform_device

of_device is just an alias for platform_device, so remove it entirely.  Also
replace to_of_device() with to_platform_device() and update comment blocks.

This patch was initially generated from the following semantic patch, and then
edited by hand to pick up the bits that coccinelle didn't catch.

@@
@@
-struct of_device
+struct platform_device

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Reviewed-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/serial/nwpserial.c b/drivers/serial/nwpserial.c
index e65b0d9..de17367 100644
--- a/drivers/serial/nwpserial.c
+++ b/drivers/serial/nwpserial.c
@@ -344,7 +344,7 @@
 
 	mutex_lock(&nwpserial_mutex);
 
-	dn = to_of_device(port->dev)->dev.of_node;
+	dn = port->dev->of_node;
 	if (dn == NULL)
 		goto out;