Revert "of/irq: of_irq_find_parent: check for parent equal to child"

This reverts commit dc9372808412edbc653a675a526c2ee6c0c14a91.

As requested by Ben Herrenschmidt:
  "This breaks some powerpc platforms at least.  The practice of having
   a node provide an explicit "interrupt-parent" property pointing to
   itself is an old trick that we've used in the past to allow a
   device-node to have interrupts routed to different controllers.

   In that case, the node also contains an interrupt-map, so the node is
   its own parent, the interrupt resolution hits the map, which then can
   route each individual interrupt to a different parent."

Grant says:
  "Ah, nuts, yes that is broken then.  Yes, please revert the commit and
   Rob & I will come up with a better solution.

   Rob, I think it can be done by explicitly checking for np ==
   desc->interrupt_parent in of_irq_init() instead of relying on
   of_irq_find_parent() returning NULL."

Requested-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: devicetree-discuss@lists.ozlabs.org
Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Cc: Tanmay Inamdar <tinamdar@apm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/of/irq.c

@@ -60,27 +60,27 @@ EXPORT_SYMBOL_GPL(irq_of_parse_and_map);
  */
 struct device_node *of_irq_find_parent(struct device_node *child)
 {
-	struct device_node *p, *c = child;
+	struct device_node *p;
 	const __be32 *parp;
 
-	if (!of_node_get(c))
+	if (!of_node_get(child))
 		return NULL;
 
 	do {
-		parp = of_get_property(c, "interrupt-parent", NULL);
+		parp = of_get_property(child, "interrupt-parent", NULL);
 		if (parp == NULL)
-			p = of_get_parent(c);
+			p = of_get_parent(child);
 		else {
 			if (of_irq_workarounds & OF_IMAP_NO_PHANDLE)
 				p = of_node_get(of_irq_dflt_pic);
 			else
 				p = of_find_node_by_phandle(be32_to_cpup(parp));
 		}
-		of_node_put(c);
-		c = p;
+		of_node_put(child);
+		child = p;
 	} while (p && of_get_property(p, "#interrupt-cells", NULL) == NULL);
 
-	return (p == child) ? NULL : p;
+	return p;
 }
 
 /**