powerpc/pseries: Add null property check to pseries_discover_pic()

The return value of of_get_property() isn't checked before it is passed
to the strstr() function, if it happens that the return value is null
then this will result in a null pointer being dereferenced.

Add a check to see if the return value of of_get_property() is null and
if it is continue straight on to the next node.
Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Reviewed-by: Chris Smart <chris@distroguy.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/pseries/setup.c

@@ -235,6 +235,8 @@ static void __init pseries_discover_pic(void)
 
 	for_each_node_by_name(np, "interrupt-controller") {
 		typep = of_get_property(np, "compatible", NULL);
+		if (!typep)
+			continue;
 		if (strstr(typep, "open-pic")) {
 			pSeries_mpic_node = of_node_get(np);
 			ppc_md.init_IRQ       = pseries_mpic_init_IRQ;