of/selftest: Fix off-by-one error in removal path

The removal path for selftest data has an off by one error that causes
the code to dereference beyond the end of the nodes[] array on the first
pass through. The old code only worked by chance on a lot of platforms,
but the bug was recently exposed on aarch64.

The fix is simple. Decrement the node count before dereferencing, not
after.
Reported-by: Kevin Hilman <khilman@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Gaurav Minocha <gaurav.minocha.os@gmail.com>
Cc: <stable@vger.kernel.org> # v3.17+

drivers/of/selftest.c

@@ -896,7 +896,7 @@ static void selftest_data_remove(void)
 		return;
 	}
 
-	while (last_node_index >= 0) {
+	while (last_node_index-- > 0) {
 		if (nodes[last_node_index]) {
 			np = of_find_node_by_path(nodes[last_node_index]->full_name);
 			if (strcmp(np->full_name, "/aliases") != 0) {
@@ -908,7 +908,6 @@ static void selftest_data_remove(void)
 				}
 			}
 		}
-		last_node_index--;
 	}
 }