powerpc: Check return value of instance-to-package OF call

On PA-Semi firmware, the instance-to-package callback doesn't seem
to be implemented. We didn't check for error, however, thus
subsequently passed the -1 value returned into stdout_node to
thins like prom_getprop etc...

Thus caused the firmware to load values around 0 (physical) internally
as node structures. It somewhat "worked" as long as we had a NULL in the
right place (address 8) at the beginning of the kernel, we didn't "see"
the bug. But commit 5c0484e2
"powerpc: Endian safe trampoline" changed the kernel entry point causing
that old bug to now cause a crash early during boot.

This fixes booting on PA-Semi board by properly checking the return
value from instance-to-package.
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Tested-by: NOlof Johansson <olof@lixom.net>
---

arch/powerpc/kernel/prom_init.c

@@ -1986,19 +1986,23 @@ static void __init prom_init_stdout(void)
 	/* Get the full OF pathname of the stdout device */
 	memset(path, 0, 256);
 	call_prom("instance-to-path", 3, 1, prom.stdout, path, 255);
+	prom_printf("OF stdout device is: %s\n", of_stdout_device);
+	prom_setprop(prom.chosen, "/chosen", "linux,stdout-path",
+		     path, strlen(path) + 1);
+
+	/* instance-to-package fails on PA-Semi */
 	stdout_node = call_prom("instance-to-package", 1, 1, prom.stdout);
+	if (stdout_node != PROM_ERROR) {
 		val = cpu_to_be32(stdout_node);
 		prom_setprop(prom.chosen, "/chosen", "linux,stdout-package",
 			     &val, sizeof(val));
-	prom_printf("OF stdout device is: %s\n", of_stdout_device);
-	prom_setprop(prom.chosen, "/chosen", "linux,stdout-path",
-		     path, strlen(path) + 1);
 
 		/* If it's a display, note it */
 		memset(type, 0, sizeof(type));
 		prom_getprop(stdout_node, "device_type", type, sizeof(type));
 		if (strcmp(type, "display") == 0)
 			prom_setprop(stdout_node, path, "linux,boot-display", NULL, 0);
+	}
 }
 
 static int __init prom_find_machine_type(void)