kobject: Export kobject_get_unless_zero()

Make the function available for outside use and fortify it against NULL
kobject.

Change-Id: I76dc2a49293ce967309a882b5067bd85b8fc828e
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
Git-commit: c70c176ff8c3ff0ac6ef9a831cd591ea9a66bd1a
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
Signed-off-by: Ritesh Harjani <riteshh@codeaurora.org>
diff --git a/lib/kobject.c b/lib/kobject.c
index 445dcae..763d70a 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -601,12 +601,15 @@
 }
 EXPORT_SYMBOL(kobject_get);
 
-static struct kobject * __must_check kobject_get_unless_zero(struct kobject *kobj)
+struct kobject * __must_check kobject_get_unless_zero(struct kobject *kobj)
 {
+	if (!kobj)
+		return NULL;
 	if (!kref_get_unless_zero(&kobj->kref))
 		kobj = NULL;
 	return kobj;
 }
+EXPORT_SYMBOL(kobject_get_unless_zero);
 
 /*
  * kobject_cleanup - free kobject resources.