[POWERPC] Fix crash in init_ipic_sysfs on efika

The global primary_ipic in arch/powerpc/sysdev/ipic.c can remain NULL
if ipic_init() fails, which will happen on machines that don't have an
ipic interrupt controller.  init_ipic_sysfs() will crash in that case.

Acked-by: Grant Likely <grant.likely@secretlab.ca>

Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/sysdev/ipic.c b/arch/powerpc/sysdev/ipic.c
index ae0dbf4..0f2dfb0 100644
--- a/arch/powerpc/sysdev/ipic.c
+++ b/arch/powerpc/sysdev/ipic.c
@@ -906,7 +906,7 @@
 {
 	int rc;
 
-	if (!primary_ipic->regs)
+	if (!primary_ipic || !primary_ipic->regs)
 		return -ENODEV;
 	printk(KERN_DEBUG "Registering ipic with sysfs...\n");