powerpc/maple: Fix comparing pointer to 0

Fixes coccicheck warning:
  arch/powerpc/platforms/maple/setup.c:232:15-16:
	WARNING comparing pointer to 0

Compare pointer-typed values to NULL rather than 0.
Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200121013153.9937-1-chenzhou10@huawei.com

arch/powerpc/platforms/maple/setup.c

@@ -232,7 +232,7 @@ static void __init maple_init_IRQ(void)
 	root = of_find_node_by_path("/");
 	naddr = of_n_addr_cells(root);
 	opprop = of_get_property(root, "platform-open-pic", &opplen);
-	if (opprop != 0) {
+	if (opprop) {
 		openpic_addr = of_read_number(opprop, naddr);
 		has_isus = (opplen > naddr);
 		printk(KERN_DEBUG "OpenPIC addr: %lx, has ISUs: %d\n",