drivers/perf: arm_pmu: avoid NULL dereference when not using devicetree

Commit c6b90653 ("drivers/perf: arm_pmu: make info messages more
verbose") breaks booting on systems where the PMU is probed without
devicetree (e.g by inspecting the MIDR of the current CPU). In this case,
pdev->dev.of_node is NULL and we shouldn't try to access its ->fullname
field when printing probe error messages.

This patch fixes the probing code to use of_node_full_name, which safely
handles NULL nodes and removes the "Error %i" part of the string, since
it's not terribly useful.
Reported-by: Guenter Roeck <private@roeck-us.net>
Signed-off-by: Will Deacon <will.deacon@arm.com>

drivers/perf/arm_pmu.c

@@ -1002,8 +1002,7 @@ int arm_pmu_device_probe(struct platform_device *pdev,
 	}
 
 	if (ret) {
-		pr_info("%s: failed to probe PMU! Error %i\n",
-			node->full_name, ret);
+		pr_info("%s: failed to probe PMU!\n", of_node_full_name(node));
 		goto out_free;
 	}
 
@@ -1023,8 +1022,8 @@ int arm_pmu_device_probe(struct platform_device *pdev,
 out_destroy:
 	cpu_pmu_destroy(pmu);
 out_free:
-	pr_info("%s: failed to register PMU devices! Error %i\n",
-		node->full_name, ret);
+	pr_info("%s: failed to register PMU devices!\n",
+		of_node_full_name(node));
 	kfree(pmu);
 	return ret;
 }