[PATCH -next] base: topology: fix unused variable compile error

[Ren Zhijie]

compile error:
drivers/base/topology.c: In function ‘topology_is_visible’:
drivers/base/topology.c:158:17: error: unused variable ‘dev’ [-Werror=unused-variable]
  struct device *dev = kobj_to_dev(kobj);
                 ^~~
cc1: all warnings being treated as errors

If CONFIG_SMP is N, the macro 'topology_ppin()'expands as follows.
"topology_ppin(dev->id) -> boot_cpu_data.ppin"
This cause an unused variable warning for 'dev' which used in the
topology_is_visible().

To fix build warning unused attribute added to the 'dev' variable.

Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Fixes:aa63a74d4535("topology/sysfs: Hide PPIN on systems that do not support it.")
Signed-off-by: Ren Zhijie <renzhijie2@xxxxxxxxxx>
---
 drivers/base/topology.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/base/topology.c b/drivers/base/topology.c
index 706dbf8bf249..70962a4bcb1f 100644
--- a/drivers/base/topology.c
+++ b/drivers/base/topology.c
@@ -155,7 +155,8 @@ static struct attribute *default_attrs[] = {
 static umode_t topology_is_visible(struct kobject *kobj,
 				   struct attribute *attr, int unused)
 {
-	struct device *dev = kobj_to_dev(kobj);
+	struct device *dev __maybe_unused;

+	dev = kobj_to_dev(kobj);
 
 	if (attr == &dev_attr_ppin.attr && !topology_ppin(dev->id))
 		return 0;
-- 
2.17.1