ext4: return an error if kset_create_and_add fails in ext4_init_fs()

In the very unlikely case that kset_create_and_add() fails when the
ext4.ko module is being loaded (or during kernel startup) set err so
that it's clear that the module load failed.

https://bugzilla.kernel.org/show_bug.cgi?id=27912

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/super.c

@@ -5285,8 +5285,10 @@ static int __init ext4_init_fs(void)
 	if (err)
 		goto out6;
 	ext4_kset = kset_create_and_add("ext4", NULL, fs_kobj);
-	if (!ext4_kset)
+	if (!ext4_kset) {
+		err = -ENOMEM;
 		goto out5;
+	}
 	ext4_proc_root = proc_mkdir("fs/ext4", NULL);
 
 	err = ext4_init_feat_adverts();