devicetree: add helper inline for retrieving a node's full name

The pattern (np ? np->full_name : "<none>") is rather common in the
kernel, but can also make for quite long lines.  This patch adds a new
inline function, of_node_full_name() so that the test for a valid node
pointer doesn't need to be open coded at all call sites.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>
diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
index 2d311c0..6b58a39 100644
--- a/arch/powerpc/platforms/pseries/iommu.c
+++ b/arch/powerpc/platforms/pseries/iommu.c
@@ -1051,7 +1051,7 @@
 	if (!pdn || !PCI_DN(pdn)) {
 		printk(KERN_WARNING "pci_dma_dev_setup_pSeriesLP: "
 		       "no DMA window found for pci dev=%s dn=%s\n",
-				 pci_name(dev), dn? dn->full_name : "<null>");
+				 pci_name(dev), of_node_full_name(dn));
 		return;
 	}
 	pr_debug("  parent is %s\n", pdn->full_name);