powerpc/mpic: Cache the device-tree node in "struct mpic"

Store the node pointer in the MPIC during initialization so that all of
the later operational code can just reuse the cached pointer.

Signed-off-by: Kyle Moffett <Kyle.D.Moffett@boeing.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/include/asm/mpic.h b/arch/powerpc/include/asm/mpic.h
index b9d2c0f..67b4d98 100644
--- a/arch/powerpc/include/asm/mpic.h
+++ b/arch/powerpc/include/asm/mpic.h
@@ -251,6 +251,9 @@
 /* The instance data of a given MPIC */
 struct mpic
 {
+	/* The OpenFirmware dt node for this MPIC */
+	struct device_node *node;
+
 	/* The remapper for this MPIC */
 	struct irq_host		*irqhost;